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A  MANUAL 

OF 

HISTOLOGY 

RADASCH 


A  MANUAL 

OF 


HISTOLOGY 


BY 

HENRY  ERDMANN  RADASCH,  M.  Sc,  M.  D. 

ASSISTANT  PROFESSOR  OF  HISTOLOGY  AND  EMBRYOLOGY  IN  THE  JEFFERSON- 
MEDICAL   COLLEGE,    AND     INSTRUCTOR    IN   ANATOMY   IN 
THE  PENNSYLVANIA  ACADEMY  OF  FINE  ARTS, 
PHILADELPHIA,  PENNSYLVANIA. 


WITH  307  ILLUSTRATIONS 


PHILADELPHIA 

P.    BLAKISTON'S   SON   &   CO. 

1012   WALNUT   STREET 


Copyright,  1918,  by  P.  Blakiston's  Sox  &  Co. 


THE  MAPLE  PKESS  XOKK  PA 


TO   MY 
FRIEND    AND    COLLEAGUE 

PROF.  RANDLE  C.  ROSENBERGER 

THIS   VOLUME    IS 
AFFECTIONATELY   DEDICATED 


PREFACE 


The  science  of  Histology  has  advanced  so  much  since  the  first 
appearance  of  the  predecessor  of  this  volume,  that  a  sufficiently  ade- 
quate presentation  of  the  subject  for  students  requires  more  space 
than  the  usual  amount  available  in  a  quiz  compend.  The  compend 
was,  therefore,  utilized  as  a  basis  for  this  expansion  and  has  been 
incorporated  into  the  text  of  the  Manual. 

The  Chapter  on  Technic,  or  Practical  Histology,  has  been  en- 
larged to  meet  the  requirements  of  routine  work  in  Laboratories  of 
Normal  and  Pathologic  Histology  and  Hematology.  The  other 
Chapters  have  been  materially  increased,  especially  that  of  the 
Nerve  System.  In  this  a  general  consideration  of  the  External 
Anatomy,  or  Morphology  of  the  Brain,  has  been  given  in  a  sequential 
manner  and  the  Internal  Anatomy,  or  Histology,  has  been  taken  up 
in  the  same  manner.  The  various  Pathways  have  been  given 
separate  consideration  so  that  this  Chapter  will  be  of  use  to  those 
studying  Neuroanatomy  and  Neuropathology. 

Many  illustrations  have  been  added  from  various  sources  and  40 
photomicrographs  have  been  utilized. 

The  writer  desires  to  thank  Dr.  J.  I.  Fanz  for  his  assistance  in 
the  preparation  of  some  of  the  photomicrographs  and  Dr.  Clarence 
Hoffman  for  the  preparation  of  the  dura  showing  Sharpey's  fibers. 
The  writer  is  also  indebted  to  the  publishers  for  their  courtesies  and 
assistance  in  the  selection  of  illustrations. 

The  author  trusts  that  this  volume  will  meet  with  the  same  appre- 
ciation and  success  as  the  compend. 

H.  E.  Radasch. 

Wynne  wood,  Pa. 


vu 


CONTENTS 

CHAPTER  I 

Page 

Technic * i 

CHAPTER  II 
The  Cell 56 

CHAPTER  III 
The  Tissues — Epithelial  Tissues 75 

CHAPTER  IV 
Connective     Tissues 101 

CHAPTER  V 
Muscle    Tissues 139 

CHAPTER  VI 
Nerve  Tissues 156 

CHAPTER  VII 
Circulatory    System 187 

CHAPTER  VIII 
Lymphatic  System      216 

CHAPTER  IX 

Alimentary  Tract 233 

CHAPTER  X 

Digestive    Glands 283 

ix 


X  CONTENTS 

CHAPTER  XI 

Page 
Respiratory  System  and  Thyreoid  Body 306 

CHAPTER  XII 
Urinary  System  and  Adrenal 323 

CHAPTER  XIII 
Male    Genital    System 35I 

CHAPTER  XIV 

Female  Genital  System 3-4 

CHAPTER  XV 

Placenta  and  Umbilical  Cord 396 

CHAPTER  XVI 
Skin  and  Its  Appendages , 411 

CHAPTER  XVII 
Nerve  System 434 

CHAPTER  XVIII 
Eyeball  and  Lacrimal  Apparatus 494 

CHAPTER  XIX 
The  Ear 526 

CHAPTER  XX 
The  Senses  of  Smell,  Taste  and  Touch 543 

CHAPTER  XXI 

Development  of  Face  and  Teeth 551 

Index 565 


PRACTICAL  HISTOLOGY 


CHAPTER  I 
TECHNIC 

For  a  thorough  understanding  of  Histology  a  knowledge  of  technic 
is  requisite,  as  sections  for  study  must  be  properly  prepared,  and  this 
requires  skill  and  care. 

Tissues  may  be  studied  in  a  fresh  or  living  condition  as  well  as 
after  fixing  and  staining.  Muscle,  tendon  and  fibrous  tissue  may 
be  placed  upon  a  slide  with  a  little  normal  salt  or  Ringer's  solution 
or  glycerin  and  gently  torn  apart  with  needles.  Ringer's  solution 
is  prepared  as  follows: 

Sodium  chlorid 90 .  o 

Potassium  chlorid " 4.2 

Calcium  chlorid  (anhydrous) 2.4 

Potassium  bicarbonate 2.0 

Distilled  water 10,000 .  o 

Peritoneum,  mesentery  or  omentum  may  be  spread  upon  a  slide, 
covered  with  salt  or  Ringer's  solution  and  a  cover-glass  and  then 
studied.  Ciliary  action  may  be  shown  by  placing  a  small  piece  of 
the  gill  of  a  clam  upon  a  slide  and  keeping  it  moist  with  salt  or 
Ringer's  solution.  The  circulating  blood  in  the  web  of  a  frog's  foot 
may  be  studied  by  using  a  special  stage  for  the  support  of  the  frog. 
The  effect  of  heat  and  cold  may  be  studied  by  the  use  of  a  special 
stage  permitting  a  flow  of  hot  or  cold  water. 

Tissues  may  be  subjected  to  the  action  of  special  agents  as  blood 
serum  and  pericardial  fluid.  Thin  sections  may  also  be  made  with 
a  double-bladed  knife  or  the  fresh  tissue  may  be  frozen  and  cut 
in  a.  special  freezing  microtome. 

1 


2  PEACTICAL   HISTOLOGY 

Maceration  is  employed  to  separate  tissues  by  dissolving  or  soft- 
ening certain  ones  and  unaffecting  others.  The  latter  may  be  iso- 
lated then  by  shaking. 

i.  Hydrochloric  Acid.  20  Per  Cent.  Aqueous  Solution. — Place 
small  pieces  of  tissue  therein  for  twenty-four  to  forty-eight 
hours  and  then  wash  thoroughly.  This  is  especially  adapted  for 
the  isolation  of  uriniferous  tubules  as  it  dissolves  the  interstitial 
tissue.  The  tubules  may  then  be  mounted  in  glycerin  jelly.  If  used 
in  the  strength  of  1  to  250  parts  of  water  this  agent  will  separate 
voluntary  muscles  fibers  at  the  discs. 

2.  Potassium  hydroxid,  as  a  20  to  40  per  cent,  solution,  acts  in 
fifteen  to  sixty  minutes  for  cells  of  the  nails,  hairs  and  epidermis. 
If  smooth  or  cardiac  muscles  are  used,  small  cubes  of  the  tissue  are 
placed  in  a  large  quantity  of  the  reagent  and  shaken.  When  dissoci- 
ation has  been  accomplished  the  tissue  is  then  transferred  to  a  satu- 
rated aqueous  solution,  of  potassium  acetate  to  neutralize  the 
hydroxid.  Later  the  tissues  are  washed  in  water,  stained  for 
twenty-four  hours  in  alum  carmin,  washed  with  water  and  mounted 
in  glycerin. 

3.  Nitric  acid  in  a  10  to  20  per  cent,  aqueous  solution  or  physio- 
logic salt  solution  may  be  used  to  isolate  muscle  fibers.  It  requires 
from  twenty-four  to  forty-eight  hours  to  act.  J.  B.  MacCallum 
recommends  the  following  for  heart  muscle:  Nitric  acid  one  part, 
glycerin  two  parts,  distilled  water  two  parts.  Small  pieces  of  tissue 
remain  from  eight  hours  to  several  days  in  this  solution  and  are 
then  transferred  to  a  5  per  cent,  aqueous  solution  of  glycerin. 

Schwalbe  recommends  a  20  per  cent,  solution  of  nitric  acid,  at 
40°C.  for  twenty-four  hours,  for  the  isolation  of  nerve  fibers  for 
measurement. 

Digestion  Method. — The  chief  agents  for  this  method  are  gastric 
juice  {pepsin)  and  pancreatic  juice  (trypsin,  or  pancreatin).  Tissues 
should  be  fresh  or  fixed  in  alcohol  only.  Pepsin  digests  collagen 
and  mucin  readily  and  elastin  slowly;  nuclein  is  only  slowly  or  not 
at  all  affected  while  keratin,  neurokeratin,  chitin,  fats  and  carbohy- 
drates not  at  all.  Pancreatin  digests  elastin,  mucin  and  nuclein 
readily;  collagen,  reticulin,  chitin,  keratin,  fats  and  carbohydrates 
are  not  affected. 


TECHNIC  3 

Tissues  to  be  digested  are  placed  in  the  solution  and  the  container 
placed  in  an  incubator  at  37°C.  for  several  hours.  The  process  may 
be  carried  on  in  a  warming  chamber  if  sections  of  tissues  are  utilized. 

Kuskow's  solution  consists  of  one  part  of  pepsin  dissolved  in  200 
parts  of  a  3  per  cent,  solution  of  oxalic  acid.  Pieces  of  hardened 
ligamentum  nuchae  are  placed  in  the  freshly  prepared  solution  and 
are  allowed  to  remain  from  ten  to  forty  minutes. 

Pancreatin. — Add  0.2  or  0.4  per  cent,  of  Mall's  or  Merck's  pan- 
creatin  to  a  0.3  per  cent,  solution  of  sodium  carbonate.  This  is 
used  to  demonstrate  reticulum  tissue  in  paraffin  sections.  Remove 
the  paraffin  with  xylol,  wash  thoroughly  in  alcohol  and  place  the 
sections  in  ether  in  a  Soxhlet  apparatus  for  several  hours  to  remove 
the  fat.  Bring  the  sections  through  graded  alcohols  to  water  and 
then  place  in  the  digesting  fluid  for  several  hours  to  several  days, 
until  all  of  the  cellular  elements  are  removed.  Wash  with  water  and 
stain  wTith  an  aqueous  solution  of  fuchsin  or  toluidin  blue,  then 
dehydrate,  clear  and  mount. 

For  reticulum  frozen  sections  40  to  80^  thick  are  placed  for  twenty- 
four  hours  in  the  following  solution:  Pancreatin  5  grams,  bicarbonate 
of  sodium  10  grams,  water  100  c.c.  Wash  carefully  with  wrater  and 
transfer  the  sections  to  a  test-tube  and  shake  thoroughly.  Then 
spread  the  tissue  carefully  upon  a  slide  to  dry.  Then  allowr  a  few 
drops  of  the  following  stain  to  dry  upon  the  section:  Picric  acid 
10  grams,  absolute  alcohol  33  c.c.,  water  300  c.c.  Stain  for  one-half 
hour  in  the  following:  Acid  fuchsin  10  grams,  absolute  alcohol  33 
c.c,  water  66  c.c.  Wash  a  moment  with  picric  acid  solution, 
dehydrate,  clear  with  xylol  and  mount  in  balsam. 

TECHNIC  FOR  FROZEN  SECTIONS 

For  cutting  sections  frozen  with  C02  the  piece  of  tissue  is  placed 
upon  the  hard  rubber  freezing  chamber  that  has  been  moistened  with 
a  little  water.  The  cylinder,  that  has  been  fastened  to  the  table, 
is  provided  with  an  outlet  tube  and  a  valve;  when  the  tissue  is  placed 
in  position  the  valve  is  gradually  opened  permitting  the  C02  to  enter 
the  freezing  chamber,  and  the  freezing  process  is  begun.  Freezing 
should  be  carried  on  cautiously.     When   the  specimen  is  frozen 


PRACTICAL   HISTOLOGY 


solid  it  is  then  set  in  the  automatic  feeding  microtome  and  cut  at 
any  desired  thickness.  Congellation  should  take  place  slowly 
and  then  sections  should  be  cut  as  nearly  4/x  in  thickness  as 
possible. 

Wright's  Method. — 1.  Place  the  fresh  specimen  in  a  10  per  cent, 
solution  of  formalin  for  about  two  hours,  or  it  may  be  boiled  for 

two  to  three  minutes  in  the  same 
solution  but  histologic  details  are 
not  so  good. 

2.  Rinse  in  water. 

3.  Cut  sections  in  the  freezing 
microtome. 

4.  Float  the  sections  upon  a 
slide,  smooth  out  and  remove  the 
surplus  water. 

5.  Place  a  sheet  of  cigarette 
paper  upon  the  section,  and  press 
this  and  the  section  down  with  a 
pad  of  soft,  smooth  filter  paper, 
the  face  of  which  has  been  moist- 
ened with  a  little  95  per  cent, 
alcohol.  Remove  the  filter  paper 
and  carefully  strip  off  the  cigarette 
paper,  leaving  the  section  adher- 
ing to  the  slide. 

6.  Flood  the  section  with  abso- 
lute alcohol  and  after  thirty  seconds  drain  it  off. 

7.  Flood  the  section  and  the  adjacent  surface  of^the^slide  with  a 
thin  solution  of  celloidin,  drain  the  excess  off  immediately. 

8.  Flood  the  slide  with  95  per  cent,  alcohol  and  then  place  the 
slide  for  ten  seconds  in  water.  This  hardens  the  celloidin  and 
prevents  the  section  from  curling. 

9.  Stain  with  hematoxylin  or  any  combination  of  stains. 

10.  Dehydrate  in  97  per  cent,  alcohol. 

11.  Clear  in  oil  of  origanum  and  mount  in  balsam. 

Rapid  Method. — Freeze  the  tissues,  with  or  without  preliminary 
hardening  in  formalin  and  cut  sections.     Transfer  the  sections  to 


Fig.     1. — Automatic     Freezing 
Microtome.     {Spencer  Lens  Co.) 


TECH  NIC 


water  and  draw  upon  a  clean  slide.  Drain  off  the  water  and  dr- 
over an  alcohol  lamp. 

Cover  with  hematoxylin  for  two  minutes,  drain  and  cover  with  a 
50  per  cent,  solution  of  lithium  carbonate  for  one  minute  (to  deepen 
the  stain).  Stain  with  Van  Gieson's  stain  for  one  minute,  wash 
with  water,  dehydrate  with  95  per  cent,  alcohol  and  the  absolute 
alcohol,  clear  with  xylol  and  mount  in  balsam. 

Some  prefer  to  infiltrate  the  tissues  with  a  gum  mucilage  and  syrup 
mixture  before  freezing. 


Fig.  2. — Freezing  Chamber.     (Spencer  Lens  Co.) 
ORDINARY  TECHNIC 

If  the  freezing  method  is  not  used  various  steps  are  necessary  to 
prepare  a  piece  of  tissue  for  sectioning,  as  Fixation,  Dehydration, 
Clearing,  Infiltration  and  Blocking. 

FIXATION 

Fixation  is  the  process  by  which  the  intercellular  substance  and 
the  protoplasm  of  the  cells  are  coagulated  by  the  aid  of  solutions, 
or  gases,  thereby  keeping  them  as  nearly  like  normal  as  possible. 
Such  solutions  are  fixing  fluids,  of  which  there  are  a  great  many 
combinations.  Simple  fixatives,  which  are  not  numerous,  will  be 
given  first,  and  under  each,  its  combinations. 

Certain  salts,  as  those  of  chromium,  osmium  and  pi  atinum,  interfere 


6  PRACTICAL   HISTOLOGY 

with  subsequent  staining  and  must  be  removed  by  thorough  washing 
after  fixation.  Alcohol,  formalin,  picric  acid,  corrosive  sublimate 
and  acetic  acid  are  either  neutral  or  favorable  to  stains. 

For  fixation,  one-quarter  inch  cubes  or  slices  of  organs,  J£  inch 
thick  and  cut  at  intervals,  are  the  most  satisfactory. 

i.  Heidenhain's  solution  consists  of  a  saturated  solution  of  bi- 
chlorid  of  mercury  in  a  normal  salt  solution. 

Bichlorid  of  mercury ,      112  gms. 

Sodium  chlorid 5  gms. 

Water 1000  c.c. 

Add  the  bichlorid  to  the  hot  salt  solution  and  when  dissolved  set 
aside  to  cool.  The  excess  of  bichlorid  will  crystallize  and  keep  the 
solution  saturated. 

Three  to  5  per  cent,  of  glacial  acetic  acid  aids  the  penetration  of  the 
bichlorid  and  assures  more  thorough  fixation. 

This  solution  requires  from  two  to  four  hours  to  fix  J^-inch 
cubes. 

2.  Potassium  Bichromate. — This  salt  in  a  solution  of  3^  per 
cent,  strength  is  a  good  fixative  and  hardener.  The  strength  is 
gradually  increased  Jlz  of  1  per  cent,  by  frequent  renewal,  to  6  per 
cent.,  in  the  course  of  six  weeks.  It  will  not  injure  tissues  left  in  it 
for  a  longer  time.  It  is  not  often  used  alone  but  in  combinations 
mentioned  below. 

(a)  Mutter's  fluid  depends  upon  potassium  bichromate  for  its 
action.     Penetration  is  aided  by  sodium  sulphate. 

Potassium  bichromate 60  gms. 

Sodium  sulphate 3°  gms> 

Water 3<*>o  c.c. 

This  solution  requires  from  three  to  six  weeks  for  fixing,  but  a 
longer  time  does  not  injure  the  tissues.  It  is  commonly  used  in  the 
dark,  and  renewed  as  often  as  it  becomes  cloudy. 

(b)  Zenker's  fluid  is  a  mixture  of  Mailer's  fluid  and  bichlorid  of 
mercury. 

Muller's  fluid 1000  c.c. 

Corrosive  sublimate 112  gms. 

Mix  and  add  before  use 

Glacial  acetic  acid 5°  c-c 


TECHNIC  7 

This  solution  requires  from  twelve  to  twenty-four  hours  to  act 
and  should  be  freshly  prepared  each  time  before  using. 

(c)  Zenker-formalin  is  made  as  follow 

Zenker's  solution go  c.c. 

Glacial  acetic  acid 5  c.c. 

Formalin 10  c.c. 

The  last  two  reagents  should  be  added  just  before  using.  This 
solution  requires  twelve  to  twenty-four  hours  for  fixation. 

Maximow  uses  10  per  cent,  formalin  in  place  of  the  acetic  acid 
and  the  results  are  said  to  be  excellent. 

Helly's  Fluid. — This  is  merely  Zenker's  fluid  in  which  the  acetic 
acid  is  replaced  by  the  same  proportion  of  formalin.  This  is  espe- 
cially adapted  for  tissues  in  which  the  granules  of  the  cytoplasm  are 
to  be  studied  (chromaffin  granules,  etc.). 

(d)  Tellyesniczky's  fluid  consists  of  a  3  per  cent,  solution  of  potas- 
sium bichromate  to  which  is  added  5  per  cent,  of  glacial  acetic  acid 
(5  c.c.  per  100).  It  is  allowed  to  act  twelve  to  twenty-four  hours 
and  then  the  tissues  are  thoroughly  washed  and  dehydrated.  Nuclei 
are  better  preserved  by  this  solution  than  by  the  usual  bichromate 
mixtures. 

(e)  Potassium  bichromate  and  formalin : 

Potassium  bichromate  (3.5  per  cent.) 90  parts. 

Formalin  (40  per  cent.) 10  parts. 

The  tissue  may  remain  in  this  solution  from  three  or  four  days  to 
two  weeks.  It  should  then  be  thoroughly  washed  and  dehydrated. 
This  solution  answers  very  wrell  for  nerve  tissues. 

3.  Chromic  acid  is  generally  used  in  0.1  to  0.5  per  cent,  solutions, 
and  should  be  allowed  to  act  one  to  eight  days,  as  it  penetrates 
slowly.  It  is  to  be  frequently  changed.  It  is  especially  adapted  to 
connective  tissues  and  where  mitotic  figures  are   to  be  studied. 

Fixation  with  chromium  salts  should  be  carried  on  in  the  dark  and 
thorough  washing  should  follow  their  use.  When  corrosive  sublimate 
is  used  the  excess  must  be  removed  before  staining.  This  may  be 
done  with  iodin  solution,  in  block  or  in  sections;  the  iodin  is  then 
removed  by  means  of  alcohol  or  weak  solutions  of  potassium  iodid 
or  sodium  thiosulphate. 


b  PRACTICAL   HISTOLOGY 

4.  Osmic  Acid. — This  reagent  is  used  in  0.5  to  1  per  cent,  solutions 
as  well  as  in  combination  with  others.  It  is  a  specific  reagent  for 
adipose  tissue,  but  if  turpentine  or  alcohol-ether  is  used  for  clearing 
the  osmicated  fat  will  be  removed.  The  time  for  fixation  depends 
upon  the  strength,  usually  from  twelve  to  twenty-four  hours  for  1 
per  cent,  solutions. 

Stock  solutions  may  be  prevented  from  reducing  by  adding  suffi- 
cient potassium  permanganate  to  impart  a  slight  violet  tint.  When 
the  solution  becomes  colorless  repeat. 

Tissues  fixed  in  osmic  acid  solution  should  be  washed  for  several 
hours  in  running  water  and  transferred  to  90  per  cent,  alcohol. 

(a)  Flemrning's  Solution : 

Osmic  acid  (2  per  cent,  solution) 4  c.c. 

Chromic  acid  (1  per  cent,  solution) 15  c.c. 

Glacial  acetic  acid 1  c.c. 

This  is  the  stronger  solution  recommended  by  Flemming. 

This  solution  which  fixes  the  tissues  in  from  one  to  two  days, 
although  a  longer  time  will  not  injure  them,  should  be  changed  at 
least  once.  The  tissues  are  then  thoroughly  washed  and  dehy- 
drated. This  fluid,  which  is  good  for  the  study  of  mitotic  figures, 
should  be  prepared  just  before  using,  as  it  does  not  keep. 

(b)  Golgi's  Solution: 

Osmic  acid  (2  per  cent,  solution) 2  parts. 

Potassium  bichromate  (2  to  2.5  per  cent. 

solution) 8  parts. 

Harden  for  three  days  in  this  solution  and  impregnate  with  silver 
nitrate  solution.  This  is  used  to  stain  nerve  cells  and  their  processes 
and  glial  cells. 

5.  Formalin  is  a  saturated  solution  of  formaldehyde  gas  in  water. 
It  is  not  used  in  full  strength,  but  usually  as  a  4  to  10  per  cent,  solu- 
tion.    A  10  per  cent,  solution  is  prepared  as  follows: 

Formalin 10  c.c. 

Sodium  chlorid  (5  per  cent,  solution) 90  c.c. 

This  requires  from  twelve  to  twenty-four  hours  for  its  action, 
and  is  especially  useful  in  the  nerve  system.  It  may  be  used  with 
potassium  bichromate  as  above  given. 


TECHNIi  9 

6.  Nitric  acid  is  used  as  a  3  per  cent,  solution,  and  small  pieces  of 
tissue  are  allowed  to  remain  therein  from  one-half  to  one  hour. 
Large  specimens  (embryos)  require  from  four  to  eight  hour-.  After 
fixation  the  tissues  are  immediately  transferred  to  70  per  cent, 
alcohol. 

It  is  especially  adapted  to  connective  tissues,  ova,  and  embryos. 

7.  Picrosulphuric  Solution  (Kleinenberg). — This  solution  is 
prepared  as  follows:  To  200  c.c.  of  saturated  aqueous  solution  of 
picric  acid  add  4  c.c.  of  concentrated  sulphuric  acid.  Allow  the 
precipitate  to  settle  then  filter.  Dilute  the  filtrate  with  600  c.c.  of 
water.     Filter  after  twenty-four  hours  if  necessary. 

This  solution  is  used  for  the  fixation  of  young  embryos  and 
delicate  tissues.  It  requires  from  one  to  twenty-four  hours.  After 
fixation  the  embryos  are  transferred  to  70  per  cent,  alcohol  until 
bleached. 

8.  Alcohol. — There  are  several  strengths  of  alcohol  suitable  for 
fixation.  Besides  acting  as  fixatives  they  at  the  same  time 
dehydrate. 

(a)  Absolute  Alcohol. — This  should  be  of  at  least  99.2  per  cent, 
strength.  It  acts  very  rapidly  and  thoroughly,  but  its  expense 
prevents  its  routine  use.  It  must  be  changed  several  times.  After 
twenty-four  to  forty-eight  hours  the  tissues  are  ready  to  be  cleared. 

(b)  Ninety-five  per  cent,  alcohol  acts  in  the  same  way  as  the  above, 
but  some  (Mallory  and  Wright)  hold  that  shrinkage  results  if  any 
solution  weaker  than  the  absolute  alcohol  is  used.  This  strength 
has,  however,  yielded  good  results  in  the  nerve  system.  It  must 
be  frequently  renewed. 

9.  Bouin's  Fluid. — This  consists  of  the  following: 

Picric  acid,  saturated  aqueous  solution 75  c.c. 

Formalin 20  c.c. 

Glacial  acetic  acid 5  c.c. 

This  solution  is  especially  applicable  to  the  fixation  of  embryos, 
small  ones  requiring  four  to  six  hours  and  large  ones  from  twenty-four 
to  forty-eight  hours.  Specimens,  after  fixation,  should  be  washed 
in  70  per  cent,  alcohol  and  then  8c  per  cent,  alcohol.  This  should  be 
changed  until  the  alcohol  is  no  longer  colored. 


IO  PRACTICAL   HISTOLOGY 

Tissues  that  have  been  fixed  in  solutions  containing  either  osmic 
acid  or  chromium  salts  must  be  thoroughly  washed  before  dehydration. 
Golgi's  method  of  staining  is  an  exception,  as  will  be  seen  when  its 
steps  are  considered. 

Blood  spreads  are  readily  fixed  in  a  solution  of  equal  parts  of 
absolute  alcohol  and  ether  in  which  they  are  allowed  to  remain 
from  twenty  minutes  to  an  hour.  Another  good  fixative  is  absolute 
alcohol,  nine  parts,  and  formalin,  one  part.  The  time  for  fixing  is 
about  the  same. 

The  blood  spreads  may  be  subjected  to  a  temperature  of  i2o°C. 
for  twenty  minutes.  Ehrlich  prefers  this  method  of  fixation  to  the 
above. 

DEHYDRATION 

After  the  tissues  have  been  fixed  in  one  of  the  above  solutions  and 
washed,  they  are  ready  for  the  second  step,  that  of  dehydration. 

Dehydration,  or  hardening,  is  the  removal  of  the  water  from  the 
tissues,  and  is  accomplished  by  alcohols  of  ascending  strengths. 
The  tissues  are  transferred  to  a  50  per  cent,  solution  for  six  to 
twenty-four  hours,  unless  otherwise  directed.  This  is  followed  by 
immersion  in  a  70  per  cent,  solution  for  the  same  time,  and  then 
in  a  95  per  cent,  solution  for  at  least  twenty-four  hours.  During 
this  time,  the  last  should  be  changed  once.  To  insure  perfect 
dehydration,  the  specimens,  after  being  drained,  may  be  placed  in 
absolute  alcohol  for  twelve  to  twenty-four  hours. 

If  the  following  steps  are  not  to  be  carried  out  immediately  the 
tissues  should  be  transferred  to  a  solution  of  70  to  80  per  cent,  alco- 
hol in  which  they  may  remain  indefinitely. 

Tissues  fixed  in  salts  of  chromium  should  be  dehydrated  in  the 
dark. 

CLEARING 

After  dehydration  is  completed  the  tissues  are  ready  for  the 
clearing  agents. 

Clearing  or  dealcoholization  is  the  process  by  which  the  alcohol 
is  removed  and  an  agent  that  will  mix  with  the  infiltration  medium 
substituted.     If  paraffin  is  to  be  used,  an  oil  or  fluid  miscible  with 


TECHNIC  1 1 

both  alcohol  and  paraffin  is  necessary;  if  celloidin  infiltration  is  to 
follow,  then  a  mixture  of  absolute  alcohol  and  ether  is  used. 

For  the  paraffin  method  the  tissues  are  removed  from  the  alcohol, 
drained  a  few  minutes  and  then  transferred,  usually  to  an  oil,  for 
twenty-four  hours.  The  oil  penetrates  the  tissues,  removes  the 
alcohol,  and  remains  in  its  place. 

Chloroform,  xylol,  and  various  oils  may  be  employed,  among  them 
being  turpentine,  which  usually  requires  twenty-four  hours  for 
half-inch  cubes. 

Xylol  requires  from  six  to  twenty-four  hours,  or  until  the  tissue  is 
transparent. 

Cedar  oil  is  used  as  follows:  The  tissues  are  first  placed  in  a  mix- 
ture of  equal  parts  of  cedar  oil  and  absolute  alcohol  for  twenty-four 
hours.  They  are  then  drained  and  placed  in  pure  cedar  oil  for  the 
same  length  of  time.  If  pure  oil  alone  is  used,  it  is  changed  several 
times  until  the  tissues  are  transparent,  which  usually  requires 
twenty-four  to  forty-eight  hours. 

INFILTRATION 

After  clearing,  the  tissues  are  ready  for  infiltration. 

Infiltration  is  the  process  by  which  the  interstices  of  the  tissue 
are  filled  with  an  agent  that  hardens  and  allows  the  tissue  to  be  cut 
without  distortion.  There  are  two  important  agents,  paraffin  and 
celloidin.  Gum  may  be  used  for  special  purposes.  The  paraffin 
method  will  first  be  considered. 

After  clearing,  the  tissues  are  drained,  blotted  with  tissue-paper, 
and  then  placed  in  a  tube  of  melted  paraffin  at  a  temperature  a  little 
above  the  melting-point,  usually  500  to  55°C.  This  is  called  paraf- 
fin No.  1,  and  its  object  is  the  removal  of  the  bulk  of  the  oil.  After 
twelve  to  twenty-four  hours  the  tissues  are  removed  to  a  tube  of 
fresh  paraffin  and  allowed  to  remain  the  same  length  of  time.  This 
is  Paraffin  No.  2,  and  the  remainder  of  the  oil  is  removed  and  pure 
paraffin  left  in  the  tissues.  The  tissues  are  then  ready  to  be 
blocked. 

By  the  use  of  chloroform,  infiltration  with  paraffin  can  be  accom- 
plished, to  a  great  extent,  in  the  cold.     The  tissues  are  completely 


12  PRACTICAL   HISTOLOGY 

dehydrated  with  absolute  alcohol  and  then  placed  in  pure  chloro- 
form to  replace  the  alcohol.  This  is  accomplished  when  the  tissues 
become  submerged,  usually  four  to  eight  hours.  They  are  then 
transferred  to  a  warm,  saturated  solution  of  paraffin  in  chloroform; 
for  two  to  four  hours,  and  then  to  pure  melted  paraffin  until  all  the 
chloroform  has  disappeared  (two  to  twelve  hours). 

If  delicate  structures  are  to  be  infiltrated  they  may  be  cleared 
slowly  by  adding  toluol,  or  benzol,  drop  by  drop,  to  the  specimen 
in  absolute  alcohol  and  mixing  after  each  addition.  By  this  method, 
2  c.c.  of  oil  can  be  added  to  the  same  amount  of  absolute  alcohol 
in  four  to  six  hours  and  no  shrinkage  result.  The  specimens  may 
then  be  transferred  to  a  mixture  of  absolute  alcohol  (one  part)  and 
toluol  (three  parts)  for  one  to  three  hours.  They  may  then  be  placed 
in  pure  toluol  from  one  to  four  hours,  the  time  depending  upon  the 
size,  one-eighth  to  one-fourth  inch  in  diameter.  From  this  it  may 
be  transferred  to  a  solution  of  paraffin  in  toluol  for  two  to  four  hours, 
after  which  more  paraffin  is  added,  and  the  tube  transferred  to  the 
paraffin-bath,  where  it  remains  for  an  hour  or  two,  and  is  then  cast. 

Acetone-paraffin  Infiltration. — Fix  the  tissues  as  usual,  place  in 
weak  alcohol  for  several  hours  and  then  transfer  to  the  following 
mixture: 

Acetone 2  vols. 

Ether 2  vols. 

Water 1  vol. 

Allow  the  tissue  to  remain  as  many  hours  as  it  is  millimeters  thick. 
Transfer  to  a  mixture  of  equal  parts  of  acetone  and  ether  saturated 
with  paraffin  (360  to  4o°C.  melting  point) .  The  tissue  should  remain 
here  twice  as  long  as  in  the  preceding  step.  Then  transfer  to  melted 
paraffin  for  five  to  ten  minutes  for  each  millimeter  of  thickness. 

BLOCKING 

Blocking  may  be  accomplished  by  the  use  of  leaden  angles,  paper 
boxes,  or  wooden  blocks.  The  leaden  angles  are  of  various  sizes  and 
are  used  in  connection  with  brass  plates.  These  are  all  cooled  in 
ice-water,  quickly  dried  and  the  angles  put  into  place.  A  small 
layer  of  paraffin  is  then  run  into  the  mold,  and  the  tissue  placed 


I  ECHNIC  13 

therein,  and  oriented.  The  mold  is  then  filled  with  melted  paraffin, 
and  as  soon  as  a  scum  is  formed,  the  whole  is  immersed  in  ice-water, 
and  the  angles  cautiously  removed,  so  that  the  water  can  act  upon 
all  sides  except  the  bottom.  Unless  this  is  done,  the  paraffin,  in 
cooling  rapidly  and  contracting,  will  enclose  water  bubbles  that  are 
unnecessary  and  annoying.  A  little  skill  is  required  to  cast  success- 
fully. Usually,  by  this  method,  the  paraffin  remains  clear,  a  condi- 
tion much  to  be  desired. 

If  blocks  are  used,  these  should  be  preferably  of  oak,  an  inch 
and  a  quarter  long,  by  seven-eighths  square.  The  end  is  carefully 
and  tightly  wrapped  with  a  strip  of  thin  paper,  forming  a  cup  % 
to  1  inch  deep.  The  specimen  is  then  quickly  oriented  upon  a 
thin  layer  of  paraffin,  and  the  cup  filled  with  paraffin.  It  is  then 
set  aside  and  allowed  to  cool.  The  enclosed  air  bubbles  rise.  The 
paraffin  is  usually  not  clear  by  this  method,  but  is  made  so  by  placing 
the  block  for  several  days  upon  paraffin  bath.  The  warmth  clears 
the  paraffin. 

After  casting,  the  blocks  are  trimmed,  and  then  are  ready  to  be 
cut  with  the  microtome. 

For  the  celloidin  infiltration  method,  fixation  and  dehydration 
are  carried  out  in  the  same  manner  as  for  paraffin,  but  a  different 
clearing  agent  is  used.  A  mixture  of  equal  parts  of  absolute  alcohol 
and  ether  will  clear  tissues  in  twenty-four  hours,  at  the  end  of  which 
time  they  are  ready  for  the  celloidin. 

Celloidin,  or  pyroxylin,  is  prepared  as  follows:  Wash  an  ounce  of 
celloidin  with  distilled  water,  dry  thoroughly,  place  it  in  a  tightly 
stoppered  container  and  cover  with  200  c.c.  of  absolute  alcohol. 
After  several  hours  add  200  c.c.  of  ether.  A  clear  solution  should 
result.  This  may  be  thinned  to  any  desired  consistency  by  the 
addition  of  a  mixture  of  equal  parts  of  absolute  alcohol  and  ether. 

After  clearing  the  tissues  are  transferred  to  the  thin  celloidin  for 
one  to  four  days.  Transfer  the  tissues  to  Stender  dishes,  cover 
deeply  with  celloidin  and  leave  the  cover  on  loosely  so  as  to  permit 
the  alcohol  and  ether  to  evaporate  slowly.  This  thickens  the  celloi- 
din and  prepares  the  tissue  for  blocking. 

The  most  satisfactory  way  of  blocking  is  to  continue  the  evapora- 
tion of  the  alcohol  and  ether  until  the  celloidin  is  fairly  firm.     Then 


14  PRACTICAL  HISTOLOGY 

place  the  dish  in  a  jar  of  80  per  cent,  alcohol  until  the  celloidin  is 
hard.  The  celloidin  should  be  transparent.  The  tissues  may  then 
be  cut  out  in  block  form  and  preserved  in  80  per  cent,  alcohol  until 
the  technician  desires  to  cut  them. 

Each  block  is  then  removed  from  the  alcohol,  dried  carefully 
and  placed,  for  a  few  seconds,  in  a  mixture  of  equal  parts  of  abso- 
lute alcohol  and  ether,  dipped  into  the  thick  celloidin  and  is  then 
placed  upon  a  wooden  block  that  has  previously  been  dipped  in  the 
alcohol-ether  and  thick  celloidin.  After  standing  a  few  minutes  in 
the  air  the  block  is  transferred  to  80  per  cent,  alcohol  until  the 
cementing  celloidin  is  hard  and  then  it  is  ready  to  be  cut.  The 
cementing  celloidin  may  be  rapidly  hardened  by  placing  the  block 
in  pure  chloroform. 

It  is  inadvisable  to  preserve  the  mounted  blocks  in  alcohol  for 
any  length  of  time  as  the  tannic  acid  of  the  wood  seems  to  affect 
the  stain  reaction  unfavorably.  Preserve  the  celloidin  blocks  in 
80  per  cent,  alcohol  until  sections  are  wanted,  then  mount  upon  the 
wooden  blocks  and  cut  immediately. 

If  the  celloidin  is  not  hard  enough,  the  blocks  may  be  placed, 
for  twenty-four  to  forty-eight  hours,  in  80  per  cent,  alcohol,  contain- 
ing 1  to  5  per  cent,  of  glycerin. 

Gum. — This  infiltration  medium  is  prepared  as  follows: 

„  f  Cane  sugar 28.5  gms. 

yrUp    \  Water 30  c.c. 

~  J  Gum  Acacia 57  gms. 

Gum      <  ,TT  . 

I  Water 310  c.c. 

Mix  together  four  parts  of  the  syrup,  five  parts  of  the  gum  and  to 
this  add  nine  parts  of  a  saturated  solution  of  boric  acid.  Filter 
through  muslin. 

The  tissues  are  thoroughly  washed  free  of  any  trace  of  alcohol, 
and  are  then  placed  in  the  above  solution,  and  allowed  to  remain 
until  penetrated,  which  requires  at  least  twenty-four  hours  if  half- 
inch  cubes  are  used.  A  longer  time  is  better.  The  process  is  aided 
by  allowing  the  jar  with  the  tissues  to  stand  in  a  warm  place. 

Tissues  infiltrated  with  gum  must  be  frozen  and  cut  in  a  freezing 
microtome. 


TECH NIC 


SECTIONING 


After  the  above  steps  have  been  finished,  the  tissues  are  ready  to 
be  sectioned. 

Paraffin  blocks  are  cut  dry,  the  knife  of  the  microtome  being  placed 
so  that  it  meets  the  block  squarely.  When  large  objects  are  cut, 
it  is  sometimes  necessary  to  place  the  knife  obliquely.  Very  thin 
sections  may  be  straightened  for  mounting  by  floating  them  on 
warm  water.     The  slide  prepared  with  Mayer's  albumen  (see  p.  53)  is 


Fig.  3. — Minot  Automatic  Rotary  Microtome. 
(Bausch  and  Lomb  Optical  Co.) 


then  dipped  beneath  them,  and  if  carefully  lifted,  the  section  rests 
smoothly  in  place  thereon. 

Celloidin  blocks  are  treated  differently.  The  knife  is  placed 
obliquely  and  kept  moist  with  80  per  cent,  alcohol.  The  block  like- 
wise is  kept  moist,  and  as  the  sections  are  cut,  they  are  transferred, 
by  means  of  a  large  sable  brush,  to  a  dish  of  the  same  strength 
alcohol,  and  allowed  to  remain  there  until  required.  If  the  celloidin 
is  too  soft,  the  sections  will  be  quite  thick.  This  may  be  remedied 
by  hardening  the  blocks  in  alcohol  containing  1  to  5  per  cent,  of 


1 6  PRACTICAL   HISTOLOGY 

glycerin.  Celloidin  answers  very  well  for  the  nerve  system,  but 
where  thin  sections  are  desired,  the  paraffin  method  is  preferable. 

Rapid  Technic. — There  is  a  rapid  method  of  technic  that  gives 
good  results.     The  steps  are  as  follows: 

i.  Fix  small  pieces  in  formol-Muller  solution  for  eighteen  to 
twenty-four   hours.     (Formol    20   c.c,    Muller's    solution   80   c.c.) 

2.  Place  in  95  per  cent,  alcohol  for  two  hours. 

3.  Fresh  95  per  cent,  alcohol  two  hours. 

4.  Absolute  alcohol  (CuSOJ,  twelve  to  twenty-four  hours. 

5.  Place  in  anilin  oil  at  52CC.  until  transparent. 

6.  Place  in  paraffin  at  46'C.  for  one  hour. 

7.  Place  in  paraffin  at  54"C.  for  three  to  four  hours. 

8.  Block. 

This  method  requires  about  fifty-six  hours. 

STAINING 

In  order  to  study  the  various  portions  of  a  cell,  they  must  be 
differently  stained.  There  are  three  classes  of  stains;  (1)  Chromatic, 
or  Nuclear,  (2)  Plasmatic,  or  Protoplasmic,  and  (3)  Special;  of 
these  two  are  generally  used — nuclear,  or  basic;  and  protoplasmic, 
or  acid.  The  nuclear  stain  is  used  first,  followed  by  the  proto- 
plasmic stain;  this  is  called  counter-staining.  Two  stains  are  used 
so  as  to  contrast  the  two  main  portions  of  the  cell. 

Stains  are  employed  in  aqueous  or  alcoholic  solutions.  The 
quality  of  an  aqueous  solution  is  better  but  an  alcoholic  stain 
penetrates  more  rapidly.  The  quality  of  the  stain  reaction  often 
depends  upon  the  fixative  used. 

Intravitam  staining  is  employed  to  tinge  the  cytoplasm  of  the 
tissues  and  cells  while  these  are  in  the  living  condition.  The  living 
nucleus  does  not  stain. 

Nuclear  Stains.- — The  most  important  of  the  chromatic  stains  are 
hematoxylin  and  the  basic  anilin  dyes.  These  depend  upon  a  color 
base  for  their  action  and  hence  the  name  basic  stains  is  sometimes 
given  to  them. 

Hematoxylin. — Silver  Hemateinate. — (a)  Dissolve  1  gram  of 
silver  nitrate  in  100  c.c.  of  distilled  water.  To  this  add  50  c.c.  of  a 
10  per  cent,  aqueous  solution  of  potassium  hydroxid.     Shake  well. 


TECUM  C  17 

Allow  this  to  stand  for  one  minute,  decant  and  wash  four  times  by 
decantation  using  150  c.c.  of  distilled  water  each  time. 

(b)  Dissolve  2.5  grams  of  hematoxylin  in  50  c.c.  of  absolute  alco- 
hol. Pour  this  upon  the  silver  oxid  and  heat  upon  a  water  bath  until 
the  mixture  boils,  shaking  frequently.  The  mixture  should  be  a 
deep  orange  color.  Filter.  To  the  filtrate  add  twenty  times  its 
volume  of  a  5  per  cent,  solution  of  potassium  alum.  The  stain  is 
ready  for  immediate  use. 

Hematoxylin  (Harris). 

Hematoxylin 1  gm. 

Absolute  alcohol 10  c.c. 

Potassium  alum  (sat.  aq.  sol.) 200  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol  and  add  it  to  the  alum 
solution.  When  this  is  brought  to  a  boil,  add  1  gram  of  mercuric 
oxid,  and  cool  the  solution  rapidly.  The  oxygen  liberated  ripens 
the  solution  immediately,  and  the  stain  is  ready  for  use  when  cool. 
It  should  be  filtered  and  diluted  with  two  to  three  times  the  quantity 
of  water,  when  ready,  and  will  require  three  to  five  minutes  stain. 

Carrazi  uses  potassium  iodate  as  an  oxidation  agent  and  claims 
that  his  stain  will  keep  for  years. 

Delafield's  hematoxylin  is  prepared  as  follows: 

Hematoxylin 4  gms. 

Alcohol 25  c.c. 

Ammonium  alum  (sat.  aq.  sol.) 400  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol,  and  add  this  solution, 
drop  by  drop,  to  the  alum  solution.  Expose  this  to  the  light  and 
air  for  a  week  or  more,  and  then  filter.     To  the  filtrate  add 

Glycerin 100  c.c. 

Methyl  alcohol 100  c.c. 

Expose  again  for  a  long  time,  and  filter.     This  solution  must  be 

diluted  three  to  four  times. 

Acid  Hematoxylin  is  made  up  as  follows : 

Hematoxylin 1  gm. 

Absolute  alcohol 30  c.c. 

Glycerin 60  c.c.      Saturated 

Water 60  c.c.  J  with  alum. 

Glacial  ecetic  acid 3  c.c. 

2 


l8  PRACTICAL  HISTOLOGY 

Add  the  glycerin  and  water  to  the  hematoxylin,  dissolved  in  the 
alcohol;  then  add  the  acid.  This  solution  must  be  exposed  to  the 
light  for  three  weeks,  when  it  becomes  bluish.  Sections  stained  in 
it  are  at  first  not  dark,  but  when  exposed  to  the  light,  they  become 
bluish. 

If  the  reaction  with  hematoxylin  is  not  deep  enough  this  may  be 
remedied  by  washing  the  section  with  a  little  dilute  alum  solution, 
or  with  water  containing  a  faint  trace  of  ammonia. 

Most  of  the  anilin  dyes  are  not  stable,  but  fade  when  exposed  to 
the  light. 

Methylene  blue  is  used  in  connection  with  the  nerve  system  and 
blood. 

Methyl  green  is  used  for  organs  and  tissues  containing  mucin, 
and  in  blood  stains. 

Safranin  O  is  the  best.  Mix  equal  parts  of  a  saturated  aqueous 
and  saturated  alcoholic  solution  using  absolute  alcohol  (Lee). 
Sections  remain  in  this  stain  from  two  to  twenty-four  hours.  They 
are  then  washed  in  plain  alcohol  for  thirty  seconds  to  differentiate. 
Clear  in  cedar  oil,  oil  of  bergamot  or  xylol  and  mount  in  balsam. 

The  author  has  found  that  the  saturated  aqueous  solution  pro- 
duces results  in  about  twenty  minutes  when  the  preceding  stain 
has  practically  no  effect. 

Bismarck  Brown. — This  stain  is  not  very  soluble  in  water.  A 
saturated  solution  is  made  by  boiling  the  stain  in  water,  and  then 
filtering.  This  gives  a  3  to  4  per  cent,  solution,  which  is  diluted 
by  adding  one-third  volume  of  absolute  alcohol.  This  stains  rapidly, 
but  does  not  overstain.  It  is  used  to  advantage  in  contrast  with 
hematoxylin,  in  connective  tissues  and  cerebellum.  It  answers 
well  in  staining  the  acid  cells  of  the  stomach.  The  sections  should 
first  be  deeply  stained  with  hematoxylin,  and  then  subjected,  five 
minutes,  to  the  above  stain.  The  acid  cells  are  distinctly  brown, 
while  the  peptic  cells  have  a  bluish  cast. 

Polychrome  methylene  blue  is  a  metachromatic  stain  and  is  used 
diluted  ten  or  even  more  times.  It  is  allowed  to  act  from  ten  to 
twenty-four  hours.  The  sections  are  then  washed  with  water, 
covered  with  water  containing  glycerin-ether  for  ten  minutes. 
They  are  then  washed  with  water,  dehydrated  with  absolute  alcohol, 


TECHNIC  I Q 

cleared  with  xylol  and  mounted  in  balsam.  This  is  an  excellent 
stain  for  plasma  and  mast  cells.  Alcoholic  fixation  is  preferable. 
The  nuclei  stain  blue,  the  granules  of  mast  cells  are  red  and  those 
of  the  plasma  cells  are  blue. 

Other  basic  stains  are  toluid'ui  blur,  thion'ni,  dahlia,  fuchsin, 
gentian  violet,  etc. 

Plasmatic,  or  Protoplasmic  Stains. — These  stain  the  cytoplasm 
and  intercellular  substance.  The  more  common  stains  are  eosin, 
Van  Gieson,  carmin  and  acid  anilin  dyes. 

Eosin  is  the  most  used  plasmatic  stain.  It  is  employed  after  the 
nuclear  stain  has  been  used  and  washed  off.  There  are  a  number  of 
eosins,  some  soluble  in  water  and  some  in  alcohol. 

Eosin  is  commonly  used  as  a  0.5  to  i  per  cent,  aqueous  or  alcoholic 
solution.  It  requires  one  to  two  minutes,  and  should  be  washed 
off  with  water,  if  an  aqueous  solution  has  been  used;  otherwise 
with  alcohol. 

Eosin  is  a  specific  stain  for  blood-cells  and  certain  granules  of  the 
leukocytes,  and  is,  therefore,  used  extensively  in  Hematology  with 
methylene  blue. 

Picric  Acid. — A  saturated  aqueous  solution  is  used  for  fifteen  to 
thirty  seconds.     It  is  then  washed  quickly  with  95  per  cent,  alcohol. 

Picrofuchsin  (Van  Gieson)  consists  of  picric  acid  and  acid  fuchsin. 

Picric  acid  (sat.  aq.  sol.) 1800  c.c. 

Acid  fuchsin  (1  per  cent,  sol.) 85  c.c. 

Stain  from  one  to  three  minutes,  and  wash  with  alcohol.  A 
little  stronger  solution  is  used  for  the  nerve  system.  Sections 
should  be  cleared  in  oil  of  origanum. 

There  are  stains  that  affect  both  nucleus  and  protoplasm  suf- 
ficiently to  differentiate  each  well.  They  are  used  chiefly  in  bulk 
staining,  especially  for  entire  embryos. 

Borax  carmin  consists  of  carmin  boiled  in  a  solution  of  borax. 

Carmin 2  gms. 

Borax  (2  per  cent.  aq.  sol.) 200  c.c. 

Boil,  and  then  add  a  few  drops  of  a  5  per  cent,  solution  of  acetic 
acid  and  100  c.c.  of  70  per  cent,  alcohol.     After  a  few  hours  fil- 


20  PRACTICAL   HISTOLOGY 

ter,  and  to  the  nitrate  add  a  small  piece  of  thymol  or  menthol,  to 
preserve. 

Allow  the  solution  to  stain  sections  for  fifteen  or  twenty  minutes, 
and  then  differentiate  with  acid  alcohol  prepared  as  follows: 

Hydrochloric  acid  (concentrated).. . i  c.c. 

Water 29  c.c. 

Alcohol  (95  per  cent.) 70  c.c. 

This  stain  is  also  used  for  bulk  staining. 

Alum  Carmin. — This  is  prepared  by  boiling  1  gram  of  carmin 
with  100  c.c.  of  a  5  per  cent,  solution  of  ammonium  alum.  This 
is  filtered  when  cool,  and  preserved  as  above.  It  also  requires  the 
same  time  for  staining. 

Picrocarmin  is  a  double  stain,  and  its  preparation  is  not  so  simple. 
It  consists  of  the  following: 

Carmin 4  gms. 

Ammonia  (concentrated) 10  c.c. 

Water 200  c.c. 

Dissolve  the  carmin  in  the  ammonia,  to  which  a  little  water  has 
been  added.  Then  add  the  water,  and,  after  twenty-four  hours, 
filter.  Allow  the  solution  to  stand  until  most  of  the  ammonia 
has  evaporated  and  add  an  aqueous  saturated  solution  of  picric 
acid  until  precipitation  occurs.  The  solution  must  be  stirred  all 
the  time.  Set  it  aside  to  crystallize  and  to  evaporate  to  one-third 
of  its  bulk.  Pour  off  the  liquid  and  evaporate  it  to  dryness.  Dis- 
solve the  first  crystals  and  evaporate  to  dryness.  This  residue,  as 
a  1  per  cent,  solution  in  water,  is  a  very  good  double  stain. 

Paracarmin  consists  of  the  following: 

Carminic  acid 1      gm. 

Aluminum  chlorid .  0.5  gm. 

Calcium  chlorid 4      gms. 

Alcohol  (70  per  cent.) 100      c.c. 

Dissolve  and  filter. 

This  stain  is  especially  useful  in  embryology,  as  it  does  not  over- 
stain,  and  may  be  used  again  and  again.  On  sections,  it  is  a  good 
contrast  stain  to  Weigert's  elastica  stain. 


TECHNIC  2 1 

Ehrlich-Biondi-Heidenhain  Stain. — This  stain  is  used  especially 

In  blood  work  or  those  tissues  containing  many  leukocytes.     It  is 

composed  of: 

Orange  (G)  (saturated  aq.  sol.) ioo  c.c. 

Acid  fuchsin  (Rubin  S)  (saturated  aq.  sol.) 20  c.c. 

Methyl  green   (00)    (saturated  aq.  sol.) 50  c.c. 

This  solution  is  diluted  to  make  a  solution  of  1-100,  which,  upon 
the  addition  of  acetic  acid,  must  be  bright  red.  It  is  difficult  to 
prepare,  and  so  is  better  bought  ready  for  use. 

Tissues  should  be  fixed  in  corrosive  sublimate,  and  sections 
stained  for  twelve  to  twenty-four  hours,  washed  with  90  per  cent, 
alcohol,  and  dehydrated  with  absolute  alcohol,  cleared  and  mounted 
in  balsam. 

Acid  fuchsin  is  quite  soluble  in  water  and  is  used  as  a  0.5  per  cent, 
aqueous  solution.  Sections  are  stained  only  a  few  minutes,  washed 
a  few  seconds  with  acidulated  water  and  then  with  alcohol,  cleared 
and  mounted.  Sections  fixed  in  chrom-osmium  fixatives  require 
twenty-four  hours  to  stain. 

Orange  G  is  readily  soluble  in  water  and  is  used  in  a  0.5  per  cent. 
solution.     It  is  of  advantage  in  blood  staining  and  in  mixtures. 

Ruthenium  red  is  used  in  a  dilute  aqueous  solution  to  stain  free- 
hand cross-sections  of  dried  tendon.  The  tendon  cells  and  the 
septa  are  stained  red  while  the  tendon  fibers  are  only  slightly  affected. 

Other  plasma  stains  are  neutral  red,  anilin  blue,  nigrosin,  light- 
green,  methyl  blue,  etc. 

Special  Stains. — Under  this  head  are  classified  (1)  those  that 
stain  by  either  depositing  a  coloring  substance  in  the  form  of  a 
precipitate  in  certain  tissues  or  spaces,  as  silver  nitrate  and  gold 
chlorid;  (2)  those  that  have  a  selective  affinity  for  certain  tissues 
as  iron  hematoxylin,  elastica,  reticulum  and  myelin  stains. 

The  metallic  stains,  silver  nitrate  and  gold  chlorid,  produce 
negative  or  positive  impregnations.  In  the  former  the  intercellular 
substances  alone  are  colored,  while  in  the  latter  the  cells  alone  are 
affected.  Lee  states  that  stock  solutions  of  nitrates  and  chlorids 
of  osmium,  uranium,  gold,  silver  and  platinum  keep  better  in  clear 
bottles  and  that  a  good  sunning  actually  improves  them.  These 
metallic  stains  are  used  only  upon  living  or  very  fresh  tissues. 


2  2  PRACTICAL   HISTOLOGY 

Silver  Staining. — Corneal  Lymph  Spaces. — In  the  solid  state 
silver  nitrate  may  be  rubbed  over  the  cornea  of  a  freshly  removed 
eveball.  This  surface  is  then  removed,  placed  in  distilled  water 
and  then  brushed  with  a  camel's  hair  brush  to  remove  the  epi- 
thelium. Expose  to  the  light  and  the  silver  nitrate  that  has  pene- 
trated the  intercellular  spaces  will  be  reduced  and  turned  black. 

Endothelial  Cells. — Remove  the  omentum,  central  tendon  of  the 
diaphragm  or  peritoneum  of  a  freshly  killed  animal,  wash  in  dis- 
tilled water  and  stretch  over  a  slide  or  nested  vulcanite  rings.  Place 
in  a  0.75  per  cent,  solution  of  silver  nitrate  until  opaque  (ten  to 
fifteen  minutes);  wash  with  distilled  water  and  expose  to  the  sun- 
light until  reddish  brown;  then  dehydrate,  clear  and  mount  in 
balsam.  The  cell  outlines  are  stained  black  and  the  nuclei  and  the 
cell  contents  are  quite  distinct. 

Vascular  Endothelium. — Into  the  aorta  of  a  narcotized  rat  or 
guinea-pig  inject  50  to  80  c.c.  of  a  1  per  cent,  solution  of  silver 
nitrate.  In  fifteen  to  twenty  minutes  follow  this  with  100  to  150 
c.c.  of  4  per  cent,  formalin  and  expose  to  the  sunlight.  When  re- 
duction is  complete  (reddish  brown)  remove  small  pieces  of  the 
mesentery,  dehydrate,  clear  and  mount  in  balsam.  The  endo- 
thelium of  the  vessels  will  be  clearly  outlined. 

Nerve  Cells  and  Processes. — Cajal-Golgi  Method. — Thin  pieces 
of  nerve  tissue  are  placed  in  the  following  solution  and  hardened 
for  three  days: 

1.  Potassium  bichromate  solution  (2  to  2.5  per  cent.) 8  parts. 

Osmic  acid  solution  (1  per  cent.) 2  parts. 

2.  Transfer  tissues  to  a  solution  of  silver  nitrate  of  }  £  to  J£  per 
cent,  strength.  First  blot  off  the  bichromate  solution  and  then 
rinse  tissues  thoroughly  in  some  silver  solution.  Then  place  tissues 
in  at  least  thirty  times  their  volume  of  silver  solution  and  allow 
them  to  stand  in  the  dark  for  three  days.  Change  the  silver  solu- 
tion after  the  first  eight  to  twelve  hours. 

3.  Return  to  the  following  solution  for  one  to  two  days: 

Potassium  bichromate  solution  (2  per  cent.) 20  parts. 

Osmic  acid  solution  (1  per  cent.) 2  parts. 


Ill   I  INK 


23 


4.  Wash  quickly  with  distilled  water  and  return  to  a  fresh  solu- 
tion of  silver  nitrate  of  previous  strength  for  thirty-six  to  forty- 
eight  hours. 

5.  Dehydrate  in  twenty  "times  the  bulk  of  95  per  cent,  alcohol 
for  twenty  minutes;  the  alcohol  should  be  renewed  after  the  first 
five  minutes. 

6.  Dehydrate  in  same  bulk  of  absolute  alcohol  for  thirty  minutes; 
renew  after  ten  minutes. 

7.  Replace  alcohol  by  same  volume  of  absolute  alcohol  and  ether 
(equal  parts)  for  twenty  minutes. 

8.  Transfer  to  thin  celloidin  for  twenty-five  minutes  and  then 
thick  celloidin  for  ten  minutes. 

9.  Block  and  harden  in  chloroform  for  about  ten  minutes. 

10.  Place  for  thirty  minutes  in  the  following  clearing  solution: 

Carbolic  acid  (melted) 50  c.c. 

Oil  of  thyme  or  cedar 50  c.c. 

Oil  of  bergamot 25  c.c. 

11.  Section,  keeping  knife  and  block  moist  with  above  clearing 
fluid. 

12.  Mount  on  slides,  remove  clearing  fluid  by  means  of  xylol, 
blot,  cover  with  thick  balsam,  but  do  not  use  a  cover-glass. 

Neurofibrils. — Bielschowsky's  Method. — Pieces  of  tissue  1  cm. 
in  size  are  fixed  in  formalin  and  placed  in  pyrodin  for  three  to  four 
days.  Wash  for  several  hours  in  frequent  changes  of  distilled  water 
and  place  in  a  3  per  cent,  solution  of  silver  nitrate  at  36°C,  for 
three  to  five  days.  Place  in  an  oxid  bath  for  twenty-four  hours. 
Prepare  this  bath  as  follows:  20  per  cent,  solution  of  silver  nitrate 
5  c.c;  40  per  cent,  solution  of  sodium  hydroxid  5  drops.  To  this 
add  sufficient  ammonia  to  dissolve  the  precipitate  and  then  add 
100  c.c.  of  distilled  water.  This  solution  keeps  only  a  few  hours 
and  should  be  prepared  just  before  use.  After  the  tissues  are 
taken  from  the  bath  wash  for  a  couple  of  hours  in  frequent  changes 
of  distilled  water  and  reduce  in  a  20  per  cent,  solution  of  formalin, 
dehydrate  and  make  paraffin  sections. 

Golgi's  Method. — Fix  fresh  nerve  tissues  for  six  to  eight  hours 
in  a  mixture  consisting  of  equal  parts  of  a  saturated  solution  of 


24  PRACTICAL   HISTOLOGY 

arsenious  acid,  96  per  cent,  alcohol  and  20  per  cent,  formalin.  Place 
for  one  to  three  hours  or  days  in  a  1  per  cent,  solution  of  silver 
nitrate.  Reduce  in  the  following:  hydroquinon  20  grams;  sodium 
sulphate  5  grams;  20 per  cent,  formalin  50C.C.;  water  1000  c.c.  Wash 
and  carry  through  celloidin.  Sections  are  to  be  toned  in  a  solution 
consisting  of  sodium  hyposulphate  30  grams;  sulphocyanid  of  am- 
monium 30  grams;  water  1000  c.c.  and  10  per  cent,  of  a  1  per  cent, 
solution  of  gold  chlorid.  Tone  until  gray  and  then  wash  carefully 
and  thoroughly,  dehydrate,  clear  and  mount. 

Silver  nitrate  solutions  (Golgi's  method)  are  also  used  for  outlining 
the  secretory  canaliculi  of  the  cells  of  the  liver,  acid  cells  of  the  stom- 
ach, etc. 

Gold  chlorid  gives  a  positive  impregnation.  It  is  used  somewhat 
for  the  study  of  lymph  spaces,  but  is  chiefly  used  upon  nerve  tissues 
for  which  it  seems  to  have  an  especial  selective  affinity.  When  it 
is  used  upon  fresh  tissues  it  is  called  pre-impregnation  and  when  it 
is  used  upon  fixed  and  hardened  tissues  it  is  called  postimpregnation. 
In  the  former  the  nuclei  are  unstained,  the  cytoplasm  is  well  stained 
and  the  axis-cylinders  are  reddish  violet.  In  the  latter  the  nuclei 
are  well  stained,  the  cytoplasm  is  pale  and  the  axis-cylinders  are 
black,  differentiating  the  neurofibrils  in  the  latter  (Lee).  It  was 
formerly  believed  that  the  tissues  must  be  fresh  for  gold  staining 
but  it  has  been  found  that  the  results  are  better  if  the  tissues  are 
put  in  a  cool  place  for  twelve  to  twenty-four  hours  before  being 
subjected  to  the  action  of  the  gold  chlorid. 

Pre  -impregnation. — Ranvier's  Formic  Acid  Method/ — Take 
four  parts  of  a  1  per  cent,  solution  of  gold  chlorid  and  one  part  of 
formic  acid  and  boil.  When  cool  place  small  pieces  of  tissue  therein: 
muscle  requires  about  twenty  minutes  and  epidermis  one  to  two 
hours  in  the  dark.  Reduce  in  the  daylight  in  acidulated  water  or 
in  the  dark  in  formic  acid  one  part,  water  four  parts,  for  twenty-four 
hours.     Infiltrate  and  make  sections  in  the  usual  way. 

Postimpregnation. — Apathy's  Method. — Fix  tissues  in  a  saturated 
solution  of  corrosive  sublimate  in  0.5  per  cent,  sodium  chlorid  and 
1  per  cent,  osmic  acid.  Infiltration  may  be  in  either  paraffin  or 
celloidin  but  should  be  rapid.  Sections  are  to  be  fixed  to  the  slide 
and  the  bichlorid  removed  with  iodin  solution  and  the  latter  removed 


TECHNIC  25 

with  alcohol.  Then  wash  the  sections  with  water,  placed  in  formic 
acid  for  one  minute  and  washed  again  with  water.  Transfer,  for 
about  twenty-four  hours,  to  a  gold  chlorid  solution  (0.1  to  1  per 
cent.),  wash  with  water  and  place  (sloping)  in  1  per  cent,  formic 
acid.  The  sections  should  face  downward  so  that  the  precipitate 
falls  away  from  them.  Reduction  is  carried  on  in  the  daylight  in 
summer  or  in  direct  sunlight  in  the  winter,  for  six  to  eight  hours 
without  a  break.  If  the  acid  becomes  brown  it  should  be  renewed. 
Lee  recommends  a  weak  solution  of  formalin,  with  or  without  the 
formic  acid,  for  the  reduction. 

Iron  Hematoxylin.— Place  sections  for  one-half  to  two  hours  in  a 
1.5  to  4  per  cent,  solution  of  ferric  sulphate  (clear  violet  crystals). 
Wash  with  water  and  stain  for  one-half  hour  in  a  0.5  per  cent, 
aqueous  solution  of  hematoxylin.  Wash  with  water  and  transfer 
to  the  ferric  sulphate  to  differentiate.  Examine  frequently  under 
the  microscope  and  continue  the  differentiation  until  the  stain  is 
removed  from  all  structures  except  the  chromatin  and  centrosomes. 
Wash  for  one-half  hour  in  running  water,  dehydrate,  clear  in  xylol 
and  mount  in  balsam.  This  stain  is  used  for  studying  the  chromatin 
and  karyokinetic  figures.  The  chromatin,  centrosomes  and  spindle 
fibers  are  black  while  the  remaining  structures  are  unstained  or 
grayish. 

Myelin  Stain. — Weigert's  Method  for  Myelin  Sheaths. — The 
tissues  are  fixed  in  bichromate,  though  this  is  not  absolutely  neces- 
sary. Results  are  more  certain  if  the  tissues  have  been  fixed  in  a 
bichromate  solution,  as  they  respond  more  readily  to  the  stains 
and  are  not  so  likely  to  fade.  Celloidin  infiltration  is  usually  the 
best. 

After  the  sections  have  been  cut,  they  are  placed,  for  four  to 
twenty-four  hours,  in  the  following  solution: 

Potassium  bichromate  5  gms. 

Chrom  alum 2  gms. 

Water 100  c.c. 

They  are  then  washed  thoroughly,  and  transferred  to  the  follow- 
ing solution  for  twenty-four  hours: 


26  PRACTICAL   HISTOLOGY 

Copper  acetate 5      gms. 

Acetic  acid  (36  per  cent.) 5      c.c. 

Chrom  alum 2.5  gms. 

Water „. 100      c.c. 

Add  the  chrom  alum  to  the  water,  bring  to  a  boil,  remove  the  heat, 
add  the  acetic  acid,  and  then  the  copper  acetate,  stirring  thoroughly 
until  the  last  of  the  salt  is  dissolved.  When  cold  the  solution  should 
be  clear. 

This  solution  is  a  mordant.  The  sections  are  carefully  washed 
and  carried  into  the  following  solution: 

Hematoxylin 1  gm. 

Absolute  alcohol 10  c.c. 

Lithium  carbonate  (sat.  aq.  sol.) 1  c.c. 

Water 90  c.c. 

The  sections  are  stained  from  fifteen  minutes  to  two  or  four  hours 
in  this  lukewarm  solution,  and  then  washed  and  left  in  the  water 
for  twelve  to  twenty-four  hours  to  deepen  the  stain.  They  are  then 
differentiated  in  the  following: 


vc  ■ 


Potassium  ferricyanid 5  gms. 

Borax  (if  granular,  use  one-half  amount; 4  gms. 

Water 200  c.c. 

In  this  solution  they  must  remain  until  the  gray  substance  becomes 
yellowish.  This  change  must  be  watched  under  the  microscope. 
The  sections  are  immediately  washed  with  water,  and  left  in  water 
for  twelve  to  twenty-four  hours,  changing  frequently.  This  fixes 
the  stain.  They  are  then  dehydrated,  cleared  and  mounted  in 
balsam. 

The  myelin  sheaths  will  be  bluish-black. 

Weigert-Pal  Method. — 1.  Fix  as  for  Weigert  method  and  after 
cutting  place  the  sections  in  a  J9  Per  cent,  solution  of  chromic 
acid  for  several  hours.  This  step  is  not  necessary  if  a  chromium 
salt  has  previously  been  used  for  fixation. 

2.  Wash  and  transfer  to  the  hematoxylin  solution  for  twenty-four 
to  forty-eight  hours.     Use  the  stain  lukewarm. 

3.  Wash  with  water  containing  about  2  per  cent,  of  lithium  car- 
bonate.    The  sections  should  be  bluish. 


TECH  NIC 


27 


4.  Differentiate  in  a  J£  per  cent,  aqueous  solution  of  potassium 
permanganate  until  the  gray  substance  of  the  nerve  tissue  is  yellow- 
ish-brown in  color. 

5.  Transfer  to  the  following  solution  until  the  gray  substance 
is  almost  colorless: 

Potassium  sulphit 1  part. 

Oxalic  acid 1  part. 

Distilled  water 200  parts. 

This  solution  requires  but  a  few  seconds  to  produce  its  action. 

6.  Wash  thoroughly  with  water,  dehydrate,  clear  and  mount. 
By  this  method  all  the  tissues,  except  the  myelin  sheaths,  are 

decolorized. 

Marchi's  Method  for  Degenerated  Nerve  Fibers. — Harden  small 
pieces  of  nerve  tissue  in  Muller's  fluid  for  one  week,  then  transfer 
for  a  few  days  to  a  mixture  of  two  parts  of  Muller's  fluid  and  one 
part  of  1  per  cent,  osmic  acid  solution.  Wash  thoroughly  with 
water,  dehydrate,  embed  in  celloidin  and  cut  sections.  Sections 
should  be  mounted  in  chloroform  balsam  to  retain  the  osmic  acid. 
The  normal  sheaths  are  yellow  while  the  degenerated  ones  are  black. 

Neuroglia,  Mallory's  Method. — Fix  fresh  nerve  tissue  for  four 
days  in  10  per  cent,  formalin  and  then  transfer  for  four  to  eight 
days  to  a  saturated  aqueous  solution  of  picric  acid.  Mordant  for 
four  to  six  days,  at  37°C.  in  a  5  per  cent,  solution  of  ammonium 
bichromate,  imbed  in  celloidin  and  section.  Place  sections  for 
fifteen  minutes  in  a  0.5  per  cent,  solution  of  potassium  permanganate, 
wash  and  transfer  for  fifteen  minutes  to  a  1  per  cent,  solution  of 
oxalic  acid.  Wash  well  and  stain  from  two  to  twenty-four  hours  in 
phosphotungstic  hematoxylin  made  as  follows:  Dissolve  1  gram  of 
hematoxylin  in  80  c.c.  of  water,  add  20  c.c.  of  a  10  per  cent,  solution 
of  Merck's  phosphotungstic  acid  and  0.2  c.c.  of  hydrogen  peroxid 
(U.S. P.).  Wash  the  sections,  dehydrate,  clear  with  oil  of  origanum 
and  mount  in  balsam.  Axis  cylinders  and  cells  are  pink  while  the 
neuroglia  is  blue. 

To  make  this  stain  permanent  after  washing  the  hematoxylin 
off  of  the  sections,  place  them  in  a  30  per  cent,  alcoholic  solution 
of  ferric  chlorid  for  five  to  twenty  minutes,  wash  with  water  and 


23  PRACTICAL   HISTOLOGY 

finish  as  above.     The  nuclei  and  neuroglia  are  clear  blue  and  other 
elements  are  yellowish  or  grayish. 

NissPs  Stain. — This  is  a  special  stain  for  the  tigroid  bodies  of 
nerve  cells.  It  responds  well  only  in  those  tissues  that  have  been 
fixed  in  95  per  cent,  alcohol. 

1.  Stain. 

Methylene  blue  (Gruebler's  B  pat.) 3.75  gms. 

Venetian  soap  (white  castile) 1.75  gms. 

Distilled  water 1000 .  00  c.c. 

2.  Differentiating  fluid. 

Anilin  oil  (pure) 10  c.c. 

95  per  cent,  alcohol 90  c.c. 

1.  Warm  the  stain  until  it  steams  and  immerse  the  sections  for 
four  to  six  minutes. 

2.  Rinse  with  distilled  water. 

3.  Differentiate  in  No.  2  until  the  sections  are  pale  blue  (twenty 
to  sixty  seconds). 

4.  Wash  with  95  per  cent,  alcohol. 

5.  Clear  in  a  mixture  of  equal  parts  of  oils  of  origanum  and 
cajeput  and  mount  in  colophonium  dissolved  in  xylol. 

The  tigroid  bodies  of  the  cytom  and  dendrites  are  a  deep  blue. 
Weigerfs   elastica   stain  is  used  to  demonstrate   the  elastic 
tissue  in  organs  and  tissues,  and  is  prepared  as  follows: 

Fuchsin 2  gms. 

Resorcin 4  gms. 

Water 200  c.c. 

This  mixture  is  brought  to  a  boil,  and  then  25  c.c.  of  a  solution  of 
liquor  ferri  sesquichlorati  added,  the  mixture  stirred  and  boiled 
for  three  to  five  minutes.  When  cool,  it  is  filtered,  and  the  precipi- 
tate dissolved  upon  the  filter,  in  200  c.c.  of  95  per  cent,  alcohol. 
This  is  stirred  and  boiled  until  the  precipitate  is  entirely  dissolved. 
The  solution  is  then  cooled  and  brought  up  to  200  c.c.  with  95  per 
cent,  alcohol  and  4  c.c.  of  hydrochloric  acid  added. 

Carbolic  acid  in  the  same  proportion  may  be  used  in  place  of 
resorcin. 


TECHNIC  29 

Sections  should  be  stained,  from  twenty  minutes  to  an  hour, 
in  this  solution,  washed  well  in  95  per  cent,  alcohol,  counter-stained 
with  picric  acid  solution  for  thirty  seconds,  washed,  dehydrated 
and  cleared  and  mounted.  The  elastic  tissue  should  be  of  a  bluish- 
black  color. 

Osmic  Acid. — This  is  used  as  a  1  per  cent,  solution  as  a  special 
stain  for  fat,  which  it  turns  black  and  renders  almost  insoluble  in 
the  ordinary  reagents  used  in  technic. 

Sudan  III. — A  solution  of  this  stain  is  also  a  special  stain  for 
fat,  coloring  it  a  deep  red.  Sections  are  stained  from  a  few  minutes 
to  twenty-four  hours  in  a  saturated  solution  of  Sudan  III  in  80 
per  cent,  alcohol.  They  are  washed  with  95  per  cent,  alcohol, 
then  water  and  mounted  in  glycerin  jelly. 

Capsicum  red  stains  the  ordinary  fat  or  the  fat  of  sebaceous  and 
ceruminous  glands,  nerve  fibers  and  fat  in  pathologic  conditions 
equally  well.  Sections  of  fixed  tissues  or  frozen  sections  may  be 
stained  five  minutes  or  longer,  washed  with  80  per  cent,  alcohol, 
then  water  and  mounted  in  glycerin  or  glycerin  jelly.  Sections 
may  be  counter-stained  with  hematoxylin.  The  stain  is  prepared 
by  making  an  alcoholic  extract  of  the  ripe  capsicum  (pericarpium 
layer)  and  evaporating  this  to  one-fifth  of  its  bulk. 

Cyanin  Solution  stains  fat  a  bluish  color. 

Picrofuchsin  (Van  Gieson). — Although  this  may  be  classed  under 
the  plasmatic  stains,  it  is,  nevertheless,  a  special  stain  for  white 
fibrous  connective  tissue.  This  it  stains  a  beautiful  bright  red, 
while  the  other  tissues  are  stained  yellowish  or  brown. 

Mallory's  Reticulum  Stain. — Sections  (bichlorid  fixation)  are 
placed,  after  the  removal  of  the  bichlorid,  in  a  0.1  per  cent,  solution 
of  fuchsin  for  one  to  three  minutes.  Wash  with  water  and  place 
in  for  five  minutes  in  a  1  per  cent,  solution  of  phosphomolybdic 
acid.  Wash  in  two  changes  of  water  and  transfer  for  five  to  twenty 
minutes  to  the  following: 

Anilin  blue  (aqueous  solution) 0.5  gm. 

Orange  G 2.0  gms. 

Oxalic  acid 2.0  gms. 

Water 100  c.c. 

Wash  with  water,  dehydrate,  clear  in  xylol  and  mount  in  balsam. 


30  PRACTICAL  HISTOLOGY 

Reticulum,  amyloid  and  mucin  are  blue  while  the  other  structures 
are  yellow  or  red. 

Amyloid  Stain. — Tissues  may  be  stained  fresh  or  after  fixation, 
preferably  in  alcohol.  Stain  sections  in  a  weak  solution  of  iodin  for 
three  minutes  and  then  wash  with  water.  Treat  with  a  i  to  5  per 
cent,  solution  of  sulphuric  acid  and  the  color  will  change  from  red 
to  blue.  Dehydrate,  clear  in  oil  of  origanum  and  mount  in  balsam. 
The  amyloid  material  will  be  blue. 

Mucin. — Fix  tissues  in  corrosive  sublimate,  imbed  in  paraffin  and 
stain  the  section,  without  removing  the  corrosive  sublimate,  for  five 
to  fifteen  minutes  in  a  dilute  solution  of  thionin  (2  drops  of  the 
saturated  solution  in  5  c.c.  of  distilled  water).  Wash  with  alcohol, 
clear  in  a  mixture  of  oil  of  cloves  and  thyme  and  then  oil  of  cedar  and 
mount  in  balsam.  The  mucin  is  red  and  the  other  substances  are 
blue. 

Muchematein  (Mayer). — This  a  special  stain  for  mucin  and 
stains  in  from  three  to  ten  minutes.     It  is  prepared  as  follows: 

Hematein 0.2  gm. 

Glycerin 40      c.c. 

Aluminum  chlorid o .  1  gm. 

Distilled  water 60      c.c. 

Mix  the  hematein  and  glycerin  in  a  mortar  and  then  add  the 
aluminum  chlorid  and  the  water.  When  mixed  add  a  drop  or  two 
of  nitric  acid  to  increase  its  sharpness  as  a  nuclear  stain. 

Glycogen. — Fix  small  pieces  of  tissue  in  the  following  for  ten  to 
twelve  hours: 

Trichloracetic  acid 9  Parts 

2  per  cent,  osmic  acid 24  parts 

Glacial  acetic  acid , 9  parts 

Distilled  water 58  parts 

Wash  with  50  per  cent,  alcohol  for  one  hour  or  longer  and  then 
imbed  in  celloidin.  Sections  are  stained  with  Best's  alkalin  carmin 
and  counter-stained  with  blue  de  Lyon  for  five  minutes  (10  grams  in 
250  c.c.  of  absolute  alcohol).  Wash  with  absolute  alcohol,  clear 
with  xylol  and  mount  in  balsam.  Fat  is  black,  glycogen  red  and 
nuclei  are  blue. 


TECHNIC  3 1 

Glycogen  is  soluble  in  water  and  alcohol  solutions  of  less  than  50 
per  cent,  strength  but  not  in  trichloracetic  acid  and  stronger  alcohols. 

Gage's  Method. — Fix  the  tissues  in  95  per  cent,  alcohol  and  embed 
in  paraffin  in  the  usual  way.  Cut  sections  and  mount  upon  slides, 
flattening  with  the  following  (Lugol's)  solution. 

Iodin 1 . 5  gms. 

Potassium  iodid 3.0  gms. 

Sodium  chlorid 1.5  gms. 

50  per  cent,  alcohol 300      c.c. 

Cover  the  section  with  this  solution,  which  acts  as  the  stain, 
for  five  to  ten  minutes,  then  dehydrate,  remove  the  paraffin  with 
xylol  and  mount  in  melted  vaselin.  To  make  the  preparation 
permanent  ring  with  shellac.  The  glycogen  granules  are  mahogany 
red. 

Mast  Cells. — Small  pieces  of  tissue  are  placed  in  the  following 
for  twenty-four  hours: 

Formalin,  40  per  cent 100  c.c. 

Alcohol,  90  per  cent 100  c.c. 

Toluidin  blue 6  gms. 

Place  for  several  hours  in  70  per  cent,  alcohol,  changing  twice. 
Transfer  to  96  per  cent,  alcohol  for  several  hours,  then  absolute 
alcohol,  benzol  and  paraffin.  In  the  sections  the  mast  cells  are  an 
intense  blue  and  sharply  outlined  upon  a  pale  blue  background. 
This  is  also  a  selective  stain  for  the  chief  cells  of  the  rabbit's  stomach. 

Plasma  Cells  and  Mast  Cells. — Sections  of  tissues,  preferably 
hardened  in  alcohol,  are  stained  for  fifteen  minutes  to  twelve  hours 
in  polychrom  methylene  blue.  Wash  with  water  and  decolorize 
with  water  containing  a  few  drops  of  glycerin-ether  for  five  to  ten 
minutes.  Wash  well  with  water,  dehydrate  in  absolute  alcohol, 
clear  with  xylol  and  mount  in  balsam.  The  nuclei  are  blue  and  the 
granules  of  the  mast  cells  are  red  while  those  of  the  plasma  cells  are 
blue. 

Mitochondria,  or  plasmosomes  are  readily  dissolved  by  acids  and 
these  must  not  be  present  in  the  fixatives  used.  For  this  reason 
Helly's  fluid  or  Flemming's  solution  (eight  days)  in  which  the 
acetic  acid  has  been  reduced  to  only  a  few  drops  are  best  adapted 


32  PRACTICAL   HISTOLOGY 

to  this  technic.  The  paraffin  sections  should  not  be  over  3/x  to  6n 
in  thickness  and  should  be  stained  by  the  iron-hematoxylin  method. 
The  mitochondria  are  seen  in  the  form  of  black  rods,  filaments  or 
granules  while  the  other  structures  are  grayish  (Meves). 

According  to  Benda's  method  fix  for  eight  days  in  Flemming's 
solution,  as  above,  and  then  wash  in  water  for  one  hour.  Then 
place  in  a  mixture  of  equal  parts  of  pyroligenous  acid  and  1  per 
cent,  chromic  acid  for  twenty-four  hours.  Transfer  to  a  2  per  cent, 
solution  of  potassium  bichromate  for  twenty-four  hours.  Then 
carry  through  paraffin  infiltration  as  usual  and  make  thin  sections. 

Mordant  the  sections  in  a  4  per  cent,  solution  of  ferric  chlorid 
for  twenty-four  hours  and  rinse  with  water.  Place  then  in  a 
solution  of  Kahlbaum's  sulphalizarinate  of  soda  (1  ex.  of  a 
saturated  alcoholic  solution  of  this  salt  in  100  c.c.  of  distilled  water) 
for  twenty-four  hours. 

Wash  the  sections  and  cover  with  crystal  violet  (saturated  solution 
of  crystal  violet  in  70  per  cent,  alcohol  one  part;  1  per  cent.  HC1 
in  70  per  cent,  alcohol  one  part;  anilin  water  two  parts);  warm 
the  sections  until  a  steam  is  given  off. 

Wash  with  water  and  differentiate  for  a  minute  or  two  in  a  30 
per  cent,  solution  of  acetic  acid,  and  then  wash  in  running  water 
for  ten  minutes. 

Blot  the  water,  dehydrate  in  absolute  alcohol,  clear  with  oil  of 
bergamot  followed  by  xylol  and  mount  in  balsam. 

Chromaffin  granules  are  readily  fixed  and  stained  by  chromic 
acid  and  salts  of  chromium.  As  these  granules  are  readily  soluble 
in  acids  these  must  not  be  present  in  the  fixative.  Helly's  fluid  is 
one  of  the  best  for  the  fixation  and  staining  of  them  especially  as  it 
permits  of  the  use  of  various  nuclear  stains.  The  granules  are 
stained  a  light  brown. 

CLEARING  AGENTS  FOR  SECTIONS 

After  sections  have  been  stained  and  dehydrated  the  alcohol 
must  be  removed  by  some  agent  that  will  permit  of  the  use  of  a 
permanent  mounting  medium.  There  are  several  of  these  de- 
alcoholization  reagents,  some  answering  better  for  some  stains 
than  others. 


TECHNIC  33 

Creosote  (Beechwood). — This  oil  clears  readily  and  may  be  used 
with  practically  all  stains.  It  has  the  advantage  of  not  dissolving 
celloidin  and  is  an  excellent  agent  for  general  laboratory  work. 
It  clears  in  from  three  to  five  minutes. 

Cedar  oil  clears  tissues  readily  from  95  per  cent,  alcohol  and  does 
not  extract  anilin  dyes. 

Oil  of  origanum  clears  readily,  celloidin  is  not  affected  but  it 
removes  anilin  dyes  somewhat.  It  is  especially  employed  after 
picrofuchsin  stain. 

Clove  oil  acts  rapidly  but  dissolves  celloidin  and  removes  anilin 
dyes.  Sections  become  hard  and  brittle  and  yellow  with  age.  It 
acts  better  when  mixed  with  an  equal  part  of  oil  of  bergamot. 

Oil  of  Bergamot  does  not  extract  anilin  dyes  nor  does  it  dissolve 
celloidin.     It  will,  however,  remove  eosin. 

Xylol,  toluol,  benzol,  all  act  very  rapidly,  and  require  dehy- 
dration with  absolute  alcohol.  They  are  useful  with  anilin  stains, 
and  are  readily  applicable  as  solvents  of  balsam.  They,  however, 
render  celloidin  stiff  and  hard. 

Carbol-xylol  is  a  mixture  of  xylol  and  carbolic  acid. 

Xylol 3    parts. 

Carbolic      acid 1    part. 

For  larger  sections,  i.e.,  brain  stem,  the  writer  prefers  the  follow- 
ing mixture: 

Carbol-xylol 2    parts. 

Clove    oil 1    to    2    parts. 

The  clove  oil  keeps  the  celloidin  soft  and  pliable  so  that  upon 
blotting  the  sections  are  flat  and  not  raised  in  ridges. 

It  acts  very  rapidly,  and  is  best  for  hematoxylin  and  carmin 
stains;  it  does  not  stiffen  celloidin. 

Anilin  oil-xylol  consists  of  anilin  oil,  two  parts,  and  xylol,  one  part. 
It  is  more  commonly  used  than  the  carbol-xylol  mixture. 

Most  of  the  oils  require  about  five  minutes  to  act.     The  sections 

are  set  aside  during  this  time.     In  the  case  of  rapidly  acting  agents, 

the  slides  are  retained  in  the  hand  and  rocked  back  and  forth  until 

the  section  is  clear.     This  is  usually  accomplished  in  a  minute 

or  so. 

3 


34  PRACTICAL  HISTOLOGY 

MOUNTING  MEDIA 
After  clearing,  the  sections  are  ready  for  the  final  step,  that  of 
mounting.     There   are   a   number   of   mounting   media,    such  as 
balsam,  dammar,  Farrant's  solution,  glycerin  jelly  and  glycerin. 

The  object  of  mounting  is  to  make  a  permanent  preparation. 
The  choice  of  medium  may  depend  upon  the  stain  used.  If  this 
is  no  factor  the  chosen  medium  should  have  a  refractive  index  as 
near  crown  glass  as  possible  (1.518).  Aqueous,  glycerin  and  glyc- 
erin jelly  mounts  may  be  made  nearly  permanent  by  preventing 
evaporation.     This  is  done  by  ringing  as  will  be  explained  later. 

Sections  and  tissues  that  cannot  be  dehydrated  and  cleared  for 
special  stain  reasons  are  mounted  in  glycerin,  syrup  or  gum. 

Glycerin  Media. — Glycerin  is  an  excellent  preserving  medium. 
When  diluted  with  water  structures  are  more  easily  examined  and 
studied  than  when  mounted  in  pure  glycerin,  but  they  are  not  so  well 
preserved.  To  preserve  in  pure  glycerin  it  is  best  to  place  the 
object  for  a  few  hours  in  a  few  drops  of  glycerin-alcohol  mixture 
(glycerin  one,  alcohol  one,  water  two  parts)  so  as  to  allow  the  gradual 
evaporation  of  the  alcohol.  It  may  then  be  covered  with  pure 
glycerin,  or  glycerin  jelly  and  then  sealed. 

Glycerin  jelly  is  a  solid  at  ordinary  temperatures  and  may  be 
softened  with  heat  and  then  poured  upon  the  object  that  has  been 
previously  treated  with  glycerin  and  water.  A  drop  is  placed  upon 
the  specimen,  and  the  cover-glass  quickly  applied,  as  this  medium 
sets  rapidly.  It  is  used  for  special  purposes,  as  for  isolated  cells, 
urinary  casts,  crystals,  etc.  Neither  dehydration  nor  clearing  is 
necessary. 

Glucose  Mixture. — Mix  forty  parts  of  glucose  and  ten  parts  of 
glycerin  in  140  parts  of  water.  Then  add  seventy  parts  of  cam- 
phorated spirits  and  filter.  This  is  especially  used  for  mounting 
sections  and  objects  stained  with  the  anilin  dyes  as  it  preserves  these 
colors.     Evaporation  may  be  prevented  by  ringing. 

Gum  and  Syrup. — Dissolve  picked  gum  arabic  50  grams,  and 
cane  sugar  (not  candied)  50  grams  in  50  c.c.  of  distilled  water  over 
a  water  bath  and  add  0.5  gram  of  thymol.  This  sets  quickly  and 
gets  as  hard  as  balsam.  It  is  used  for  mounting  preparations 
stained  with  methylene  blue. 


TECHNIC  35 

Farrant's  medium  consists  of  4  ounces  of  picked  gum  arabic,  4 
ounces  of  water  and  2  ounces  of  glycerin.  Sections  are  covered 
with  this,  a  cover-glass  applied  and  later  a  cement  ring  is  put  on. 

Resinous  Media. — These  media  comprise  gum  sandarac,  Canada 
balsam,  gum  dammar  and  colophonium.  These  are  all  solids  and 
are  liquefied  by  the  action  of  certain  volatile  solvents. 

Euparal  is  a  new  mounting  and  preserving  medium.  This  is  a 
mixture  of  camsal,  sandarac,  eucalyptol  and  paraldehyde.  It  is 
colorless  or  greenish,  dries  slowly  and  is  considered  better  than 
balsam  (Lee).  The  sections  can  be  mounted  directly  from  95 
per  cent,  alcohol  without  clearing,  or,  after  dehydration,  the  sec- 
tions may  be  treated  with  isobutylic,  or  propylic  alcohol  and  then 
mounted  in  euparal. 

Balsam. — Sections  to  be  mounted  in  balsam  must  be  thoroughly 
dehydrated  and  cleared  in  an  oil.  The  oil  is  then  removed  by 
blotting,  a  small  drop  of  balsam  placed  upon  the  specimen  and  a 
clean  cover-glass  applied. 

The  balsam  is  soluble  in  chloroform,  turpentine,  benzol  or  xylol. 
The  latter  agent  is  the  best.  Sections  mounted  in  this  medium 
are  permanent. 

Dammar  is  more  complex.     It  consists  of  the  following: 

Gum    dammar 1^  oz. 

Gum    mastic %  oz. 

Turpentine 2  oz. 

Chloroform 2  oz. 

The  dammar  is  to  be  dissolved  in  the  turpentine,  and  the  mastic 
in  the  chloroform.  Each  is  to  be  filtered,  the  filtrates  mixed  and 
the  mixture  filtered.  This  is  to  be  kept  in  a  well-stoppered  bottle 
to  prevent  the  evaporation  of  the  chloroform. 

Colophonium. — Pale  colophonium  is  dissolved  in  pure  turpentine 
to  form  a  solution  of  medium  consistency.  This  sets  slowly  and  is 
injurious  to  alum  hematein  stains,  but  is  excellent  for  methylene 
blue  and  other  general  stains. 

After  the  sections  are  ready  for  mounting  a  drop  or  two  of  the 
selected  mounting  medium  is  placed  upon  the  object  and  a  clean 
cover-glass  applied. 


36  PRACTICAL   HISTOLOGY 

Cements. — Aqueous  and  glycerin  mounts  are  rendered  permanent 
by  painting  the  clean  edges  of  the  cover-glass  with  a  layer  of  glycerin 
jelly  and  repeating  this  several  times,  allowing  each  coat  to  set. 
This  seals  the  cover-glass.  This  may  be  followed  by  a  mixture  of 
gold  size  one  part,  dammar  two  parts,  dissolved  in  benzol.  Several 
rings  of  this  are  applied  at  intervals  of  twenty-four  hours. 

Shellac  cement  for  ringing  may  be  made  by  dissolving  shellac  to 
the  desired  consistency  in  wood  alcohol,  or  naphtha.  Add  20  drops 
of  castor  oil  to  each  ounce. 

DECALCIFICATION 

Bone  and  teeth  may  be  ground  for  study.  If  sections  are  desired, 
the  inorganic  substance  must  be  removed  by  means  of  acids.  This 
process  is  decalcification. 

Whole  teeth  and  small  pieces  of  bone  are  fixed  and  hardened  in 
solutions  containing  a  salt  of  chromium,  and  are  allowed  to  remain 
as  long  as  required.  After  being  thoroughly  washed  and  dehydrated 
as  above,  they  are  ready  for  the  decalcifying  agent,  of  which  large 
quantities  are  to  be  used.  The  solutions  given  below  are  the  most 
important. 

Phloroglucin-nitric  acid  is  no  doubt  the  best.     It  consists  of 

Phloroglucm 1  gm. 

Nitric  acid  (concentrated) 5  c.c. 

Alcohol  (70  per  cent.) 100  c.c. 

The  phloroglucin  is  dissolved  in  the  nitric  acid,  and  allowed  to 
stand  until  the  fumes  have  disappeared  (about  twenty-four  hours). 
The  alcohol  is  then  added,  and  then  5  to  10  per  cent,  of  nitric  acid. 
The  teeth  or  bone  are  placed  therein  until  readily  penetrated  by  a 
needle  or  cut  with  a  scalpel.  The  tissues  are  then  transferred  to 
alcohol  and  dehydrated  in  the  manner  already  stated.  Celloidin 
is  the  better  infiltrating  agent,  as  heat  tends  to  harden  osseous 
tissues.  Additional  nitric  acid  may  be  added  from  time  to  time  as 
the  solution  weakens. 

Mayer's  solution  is  a  5  per  cent,  solution  of  nitric  acid  in  95 
per  cent,  alcohol.  It  acts  very  well.  The  alcohol  is  supposed  to 
prevent  swelling  of  the  tissues. 


TECIINIC 


37 


Trichloracetic  Acid. — A  5  per  cent,  solution  of  this  is  used.  It 
is  slower  than  the  nitric  acid,  but  the  treatment  is  the  same. 

Picric  acid  in  a  saturated  aqueous  solution  is  only  adapted  to  small 
objects  as  young  embryos  and  is  a  very  slow  reagent.  It  must  be 
frequently  renewed.  Picronitic  and  picrohydrochloric  acids  act 
more  rapidly. 

Decalcification  may  be  carried  on  after  the  tissues  have  been 
imbedded  in  celloidin.  The  celloidin  block  is  transferred  to  a  10  to 
40  per  cent,  solution  of  nitric  acid  in  85  per  cent,  alcohol  and  allowed 
to  remain  until  decalcification  is  complete.  Then  the  block .  is 
washed  in  85  per  cent,  alcohol  containing  precipitated  carbonate 
of  calcium  to  neutralize  the  acid.  The  tissue  is  then  ready  to 
be  mounted  upon  a  wooded  block  and  cut.  This  is  an  excellent 
method  for  the  temporal  bones  of  mammals. 

GRINDING 

Macerate  a  tooth  or  a  piece  of  fresh  bone  to  remove  the  fat  and 
soft  parts.  Saw  thin  sections  and  cement  them  to  a  glass  plate 
with  sealing  wax.  Grind  to  one-half  the  thickness  on  a  fine  emery 
wheel.  Unseal  and  reseal  the  ground  side  toward  the  plate  and 
grind  the  section  until  quite  thin.  Remove  the  section  carefully 
and  rub  upon  a  water  hone  to  the  desired  thinness,  then  wash,  dry 
thoroughly  and  mount  in  balsam. 

Dry  Method. — Cut  sections  one-sixteenth  of  an  inch  thick  with 
a  jeweler's  saw.  Place  this  section  near  the  end  of  a  microscope 
slide,  heat  some  shellac  just  to  the  melting  point  and  pour  it  around 
the  section  to  form  a  zone  about  one-half  inch  wide.  Be  sure  to 
press  the  section  firmly  against  the  slide  while  the  shellac  is  setting 
so  as  to  prevent  any  of  this  from  getting  under  the  section.  The 
grinding  is  done  upon  sand,  emery  or  carborundum  papers^according 
to  the  hardness  of  the  substance  to  be  ground.  Sandpaper  Nos.  2, 
1,  00  and  0000  are  the  best  grades.  Brittle  substances  grind  best 
upon  No.  00  using  a  light  touch.  Tougher  substances  should  be 
started  upon  Nos.  2  and  1.  During  grinding  the  index  finger 
of  the  hand  holding  the  slide  should  be  placed  back  of  the  section 
so  as  to  insure  uniform  pressure  to  all  parts  of  the  section.     The 


38  PRACTICAL  HISTOLOGY 

section  should  be  moved  in  an  elliptical  manner  and  the  paper  kept 
free  of  the  particles  resulting  from  the  grinding.  When  this  surface  is 
ground  true  it  is  finished  upon  No.  0000.  Polishing  is  accomplished 
by  rubbing  the  ground  surface  first  upon  the  back  of  a  piece  of  sand- 
paper, then  upon  a  piece  of  smooth  ground  glass,  upon  the  palm  of 
the  hand  or  upon  a  razor  strop. 

After  gringing  one  surface  the  section  is  removed  by  first  chipping 
the  shellac  away  from  the  edge  and  then  soaking  the  specimen  in 
95  per  cent,  alcohol  or  wood  alcohol.  When  the  shellac  is  softened 
the  section  may  be  lifted  by  slipping  a  safety  razor  blade  under 
it  and  lightly  lifting  the  section  to  another  clean  slide.  The  polished 
surface  is  then  cemented  to  the  glass  as  above.  As  the  second  grind- 
ing proceeds  the  section  may  be  examined  under  the  microscope 
from  time  to  time  until  the  desired  thinness  has  been  attained.  As 
the  section  becomes  thinner  greater  precaution  must  be  taken  in 
grinding.  This  surface  is  then  finished  as  before.  To  remove  the 
section  place  the  slide  horizontally  in  a  Petri  dish  of  95  per  cent, 
alcohol  for  four  or  five  hours  if  necessary.  The  section  may  then  be 
stained  in  the  regular  manner,  or  the  section  may  be  dried  and 
mounted  in  balsam. 

This  method  was  devised  by  Dr.  J.  I.  Fanz  in  the  preparation  of 
a  hard  and  brittle  plant  stem  where  all  other  methods  absolutely 
failed.  The  results  of  this  method  were  exceptionally  good  and  the 
method  works  equally  well  with  bone,  shell,  etc. 

INJECTION 

Injection  Masses. — In  order  to  study  the  circulatory  system,  the 
vessels  must  be  injected  with  a  substance  that  will  outline  them. 
For  this  purpose,  either  an  aqueous  solution  of  carmin  or  of  Berlin 
blue,  or  gelatin  masses  are  used. 

Berlin  blue  is  used  in  water,  one  part  to  twenty,  and  this  is  in- 
jected with  a  hand  syringe  or  by  continuous  air  pressure.  It  gives 
very  good  results. 

The  gelatin  masses  may  be  either  carmin  or  Prussian  blue,  or 
Berlin  blue. 

The  carmin  mass  consists  of  the  following: 


TECHNIC  39 

Carmin 2     gms. 

Water. 

Ammonia. 

Stir  the  carmin  in  a  little  water,  and  add  strong  ammonia,  drop 
by  drop,  until  the  carmin  is  entirely  dissolved.  Filter  the  solution 
and  add  it  carefully  to  the  melted  gelatin.  The  latter  is  prepared 
by  soaking  gelatin  in  double  its  quantity  of  water,  and  melting. 
The  mixture  is  stirred  and  then  neutralized  with  dilute  acetic  acid. 
If  too  acid,  the  carmin  will  be  precipitated,  and  if  the  ammonia  is  not 
neutralized  and  the  gelatin  is  quite  alkaline,  the  stain  will  not  be 
limited  to  the  injected  vessels,  but  will  be  diffused  into  the  sur- 
rounding tissues. 

This  mass  should  be  filtered  while  hot,  and  preserved  with  a  little 
camphor. 

The  Prussian  blue  mass  is  somewhat  similar.  Four  gms.  of 
the  Prussian  blue  are  stirred  into  80  c.c.  of  water,  and  the  mixture 
added  to  gelatin  prepared  as  above.  The  solution  is  filtered  while 
hot,  and  preserved  with  camphor,  or  covered  with  methyl  alcohol. 

The  entire  body,  or  individual  organs,  may  be  injected.  When 
the  hand  syringe  is  used,  great  care  must  be  exercised  that  the 
pressure  be  not  too  great,  as  the  vessels  will  rupture  and  the  mass 
extravasate.  The  continuous  air  pressure  method  is  the  better. 
The  mass  must  be  melted  and  the  animal  kept  warm  by  immersion 
in  warm  water.  As  soon  as  the  injection  is  complete,  the  animal 
or  organ  is  immersed  in  ice-water,  so  that  the  gelatin  may  set  imme- 
diately. When  the  body  is  cooled,  the  organs  are  cut  into  blocks, 
and  transferred  to  80  per  cent,  alcohol,  where  they  remain  until 
thoroughly  hardened,  which  takes  from  one  to  three  days.  The 
addition  of  5  per  cent,  of  formalin  will  hasten  the  hardening.  They 
are  then  treated  with  95  per  cent,  alcohol  to  dehydrate,  then  cleared 
and  infiltrated  like  any  other  tissue. 

White  Mass. — Precipitate  125  to  185  c.c.  of  a  cold  saturated 
solution  of  barium  chlorid  by  adding  sulphuric  acid  drop  by  drop. 
Allow  the  precipitate  to  settle  for  twenty-four  hours  and  decant 
the  clear  fluid.  The  remaining  mucilaginous  mass  is  mixed  with 
an  equal  volume  of  strong  gelatin  solution. 

Yellow  Mass. — Mix  equal  volumes  of  concentrated  gelatin  solution 


40  PRACTICAL   HISTOLOGY 

and  a  4  per  cent,  solution  of  silver  nitrate  and  warm;  add  a  small 
quantity  of  pyrogallic  acid  which  reduces  the  silver  rapidly.  Then 
add  5  to  10  per  cent,  by  volume,  of  glycerine  and  2  per  cent,  by 
weight,  of  chloral  in  a  concentrated  solution  and  strain.  This 
mass  is  vellow  in  the  capillaries  and  brown  in  the  larger  vessels. 

Self  Injection  of  Living  Animals. — This  is  accomplished  by 
allowing  a  definite  quantity  of  blood  to  escape  from  an  opening  in  a 
vein  of  a  living  animal  and  replacing  the  lost  blood  by  some  innocu- 
ous coloring  substance;  in  this  way  the  contractions  of  the  heart 
fills  the  vessels  with  much  less  injury  than  in  the  injection  methods. 

Dissolve  7.75  grams  of  carmin  in  3.6  c.c.  of  ammonia  and  add  30 
c.c.  of  distilled  water.  Filter.  Remove  10  c.c.  of  blood  from  the 
jugular  vein  of  a  rabbit  and  then  inject  10  c.c.  of  the  above  solution. 
If  the  larger  vessels  are  then  rapidly  ligated,  first  the  vein  and  then 
the  arterv,  a  physiological  injection  of  the  vessels  will  be  obtained. 
The  injection  may  also  be  accomplished  by  placing  the  above  fluid 
in  the  stomach,  rectum  and  abdominal  cavity.  After  the  injection 
has  been  accomplished  the  organs  are  placed  in  acidulated  alcohol 
to  cause  the  fixation  of  the  carmin. 

For  staining  the  tubules  of  the  kidney  Heidenhain  uses  a  cold 
saturated  solution  of  either  indigo  blue  sulphate  or  phenizine  sul- 
phate of  sodium.  Inject  25  to  50  c.c.  of  this  into  the  vein  of  a  me- 
dium sized  rabbit  or  50  to  75  c.c.  into  a  medium  sized  dog.  After  the 
animal  has  passed  blue  urine  for  some  time  it  is  killed  by  bleeding 
and  the  coloring  matter  is  fixed  by  injecting  the  kidney,  with  abso- 
lute alcohol,  through  the  renal  vessels. 

Intravitam  Injection. — Heat  1  gram  of  rectified  methylene  blue 
in  100  c.c.  of  normal  salt  solution;  allow  this  to  cool  and  then  filter. 
Some  of  this  may  be  injected  into  the  vena  cutanea  magna  of  a 
living  frog  and  the  organs  removed  in  one  hour  and  treated  as  given 
below.  Twenty  c.c.  of  the  solution  may  be  injected,  subcutaneously, 
into  a  voung  rabbit  and  repeated  in  one  hour.  At  the  end  of  two 
hours  the  animal  may  be  killed  and  the  nerve  system  removed. 
Organs  may  be  injected  with  the  same  solution  until  they  have  a 
bluish  color,  then  they  are  left  undisturbed  for  one  hour. 

Place  pieces  of  such  tissue,  not  over  3  mm.  in  thickness,  into  a 
saturated  aqueous   solution  of   ammonium  picrate   for  forty-five 


TECHNIC  41 

minutes.  Transfer  to  a  solution  of  ammonium  molybdate  (1  gram 
to  100  c.c.  of  water  and  10  c.c.  of  a  0.5  per  cent  solution  of  osmic 
acid)  for  four  to  twelve  hours.  Wash  thoroughly  with  water,  dehy- 
drate, clear  in  xylol  and  imbed  in  paraffin.     Section. 

Corrosion. — In  order  to  study  the  normal  cavities,  the  distribution 
and  arrangement  of  ducts  and  blood-vessels  in  an  organ,  a  special 
mass  is  injected  and  the  soft  parts  removed,  thereby  leaving  a  cast 
of  the  system  injected.  The  mass  should  fuse  at  a  low  temperature 
(water  bath)  and  should  not  soften  at  the  high  temperature  of  the 
summer  months.  It  should  take  color,  readily,  should  harden 
rapidly  and  uniformly  without  cracking. 

One  of  the  best  mixtures  consists  of  ozokerite  two  parts,  paraffin 
(450  to  5o°C.)  two  parts  and  white  wax  one  part.  For  coloring  it  is 
advisable  to  use  the  various  oil  colors  put  up  in  tubes.  These  are 
added  slowly  to  the  melted  mass  with  constant  stirring.  The  various 
colors  are  English  vermilion,  ultramarine  blue,  Prussian  blue,  purple 
lake,  chrome  green,  chrome  yellow,  Chemnitz  white,  etc. 

A  solid  metal  syringe  of  sufficient  capacity  for  each  injection  should 
be  utilized  and  the  canula  should  narrow  abruptly  at  the  point. 
The  blood  is  removed  from  the  organ  by  washing  and  milking  the 
vessels  and  if  fine  injections  are  desired  it  is  best  to  float  the  organ 
in  warm  water.  As  soon  as  the  injection  is  completed  the  organs  are 
cooled  as  rapidly  as  possible.  They  are  then  freed  of  any  water  in 
the  vessels  and  placed  in  a  dish  and  gradually  surrounded  with 
fuming  commercial  hydrochloric  acid.  At  first  a  glass  plate  should 
cover  the  dish  which  should  stand  in  the  open  air  or  under  a  chemical 
hood.  The  time  required  varies  from  several  days  to  a  week  and  as 
long  as  the  acid  fumes  it  may  be  used  again.  Remnants  of  the 
organ  may  be  removed  by  cautiously  washing  the  cast. 

BLOOD  TECHNIC 

Blood  is  drawn  from  the  finger  tip  or  lobe  of  the  ear.  The  part 
is  thoroughly  cleansed  and  finally  washed  with  alcohol.  A  sterilized 
needle  is  then  plunged  to  a  depth  of  about  one-eighth  of  an  inch,  and 
the  blood  allowed  to  flow.  The  part  should  not  be  squeezed,  as  this 
dilutes  the  blood  with  lymph,  and  causes  errors  in  accurate  work. 


42 


PRACTICAL   HISTOLOGY 


Blood  spreads  are  obtained  by  touching  a  drop  of  blood  with  a 
cover-glass,  and  immediately  placing  this  upon  a  second  glass. 
The  two  are  then  slid  apart,  so  that  a  thin  film  of  blood  is  present 
upon  each.  If  the  glasses  are  lifted  apart,  the  cells  are  greatly 
distorted  and  useless  for  study.  A  better  way  is  to  place  a  drop  of 
blood  upon  one  slide  and  then  drag  this  drop  across  the  slide  with 


Fig.  4. — Drawing  Apart  the  Cover-glass.     (Da  Costa.) 

the  short  edge  of  another  slide;  this  gives  a  more  extensive  and  a 
more  even  spread. 

The  spreads  are  allowed  to  dry  in  the  air,  and  then  fixed  by  (1) 
heatj  (2)  the  absolute  alcohol-formalin  solution,  or  (3)  absolute 
alcohol-ether  mixture. 


Fig.  5. — The  Cover-glasses  after  Separation.     (Da  Costa.) 

If  heat  is  used,  the  spreads  are  placed  in  an  oven,  and  kept  at  a 
temperature  of  i2o°C.  for  twenty  minutes.  Ehrlich  prefers  this 
method. 

The  alcohol-ether  mixture  consists  of  equal  parts  of  absolute 
alcohol  and  ether.  This  fixes  the  spreads  in  twenty  minutes.  Results 
with  this  fixative  are  very  good. 

The  alcohol-formalin  mixture  consists  of  nine  parts  of  absolute 


TECHNIC  43 

alcohol  and  one  part  of  formalin.  Spreads  are  fixed  in  twenty 
minutes. 

After  fixation,  the  spreads  are  allowed  to  dry,  and  may  then  be 
stained  like  any  other  tissue.  Hematoxylin  and  eosin  give  a  good 
result. 

Among  special  stains  is  the  Ehrlich-Biondi-Heidenhain  stain. 
For  its  composition,  see  stains,  p.  21. 


Fig.  6. — Preparation'Xof^Smears_\vith    Two    Glass   Slides.     {Da   Costa.) 


Wright's  blood  stain  is  one  of  the  most  satisfactory,  and  is  pre- 
pared in  the  following  manner: 

Steam  1.5  grams  of  methylene  blue  in  150  c.c.  of  a  1  per  cent, 
aqueous  solution  of  sodium  bicarbonate  for  one  hour,  in  a  sterilizer. 
Add  a  J-10  per  cent,  aqueous  solution  of  yellowish  eosin  to  100  c.c. 
of  the  methylene  blue  solution  until  the  mixture  turns  purple,  and 
a  yellowish  metallic  scum  forms  upon  the  surface,  and  a  blackish 
precipitate  appears;  about  500  c.c.  of  eosin  solution  will  be  required, 
and  it  should  be  added  slowly,  while  constantly  stirring.  The 
solution  is  then  filtered,  the  precipitate  dried  and  made  into  a 
saturated  solution  with  methyl  alcohol.  This  solution  is  filtered 
and  80  c.c.  of  the  nitrate  are  diluted  with  20  c.c.  of  methyl 
alcohol. 

Dried  spreads  are  stained  for  one  minute  with  this  solution,  and 
the  stain  then  diluted  upon  the  glass,  with  water,  until  the  stain  is 
semi-transparent.  After  two  or  three  minutes,  the  spreads  are  thor- 
oughly washed  with  distilled  water,  dried  quickly  and  mounted. 
The  acidophilic  granules  are  reddish-lilac  and  red,  while  the  baso- 
philic granules  are  deep  blue  or  even  black. 

This  solution  hoih  fixes  and  stains  the  cells. 

Leischman's  stain  is  a  modification  of  Wright's.  It  can  be  pur- 
chased in  solid  form  and  is  verv  satisfactory. 


44  PRACTICAL   HISTOLOGY 

Eosin  and  methylene  blue  give  good  results.  The  spreads  are 
stained  in  a  J-£  per  cent,  alcoholic  solution  of  eosin  for  two  or  three 
minutes,  using  gentle  heat.  Then  they  are  placed  in  a  saturated 
aqueous  solution  of  methylene  blue  for  two  or  three  minutes.  The 
spreads  are  then  thoroughly  washed,  dried  and  mounted  in  balsam. 
As  a  rule,  the  granules  of  the  leukocytes  are  well-stained. 

In  order  to  obtain  the  bell-shaped  red  cells,  the  finger  should  be 
thoroughly  cleansed,  and  the  blood  drawn  as  usual.'  The  first 
drop  should  be  wiped  off  and  a  drop  of  i  per  cent,  osmic  acid  solution 
placed  over  the  puncture.  The  blood  then  flows  into  the  osmic 
acid,  which  acts  as  a  fixative,  and  prevents  contact  with  the  air  until 
fixation  is  complete.  If  this  drop  be  examined  under  the  micro- 
scope, the  bell-shaped  cells  will  be  seen  in  great  numbers. 

Blood  platelets  may  also  be  stained  in  the  above  way. 

Erythroblasts  of  the  spleen  may  be  studied  in  spreads  made  by 
drawing  thin  pieces  of  the  organ  over  cover-glasses.  These  are  then 
fixed  in  the  following: 

Mercuric  chlorid 78  grs. 

Sodium  chlorid 28  grs. 

Water 30  c.c. 

This  solution  should  be  filtered,  and  spreads  fixed  in  it  for  one 
minute.     They  should  then  be  washed  and  stained  one-half  hour 


Fig.  7. — Thoma-Zeiss  Counting  Chamber. 


with  aqueous  hematoxylin,  washed  and  covered  with  a  3  per  cent. 
solution  of  eosin  for  two  to  three  minutes.  They  are  then  washed, 
dried  and  mounted. 

Spreads  may  be  stained  for  three  minutes  with  eosin,  and  one- 


TECHNIC 


45 


half  minute  with  5  per  cent,  methylene  blue,  then  washed,  dried 
and  mounted. 

To  determine  the  number  of  blood-cells  the 
hemocytometer  is  used.  This  consists  of  a  heavy 
glass  slide,  a  heavy  cover-glass  and  two  pipets.  In 
the  middle  of  the  slide  there  is  a  small  disc  of 
glass  upon  which  are  marked  400  squares  each 
side  of  which  is  3^0  mm-  m  length,  making 
Jioo  sci-  mm-  square  surface  for  each  square. 
Surrounding  the  disc  is  a  glass  ring  that  is  }?{q 
of  a  mm.  higher  than  the  disc  so  that  when  the 
heavy  cover-glass  is  in  place  the  cubic  content 
over  each  small  square  is  Jiooo  of  a  cu.  mm. 

The  stem  of  the  pipet  for  counting  the  red 
blood-cells  is  so  graduated  that  it  constitutes 
Moo  °f  the  cubic  contents  of  the  bulb  por- 
tion; above  the  bulb  is  a  mark  101.  The  blood 
to  be  examined  is  drawn  to  the  mark  1  (just 
below  the  bulb)  and  then  the  diluting  and 
staining  fluid  is  drawn  to  the  mark  101,  giving, 
thus,  a  dilution  of  100.  The  contents  of  the 
bulb  are  then  thoroughly  mixed  by  means  of 
a  small  glass  pearl  in  the  bulb  and  the  diluted 
blood  is  then  ready  to  be  examined.  The  pipet 
used  for  counting  the  white  cells  is  constructed 
for  a  dilution  of  only  ten  times. 

For  the  dilution  of  the  blood  the  following 
solutions  may  be  used: 


Toison's  Fluid. 


Fig.  8. — Thoma- 
Zeiss  Capillary 
Pipets. 

A,  Erythrocytometer; 
B,  Leucocytometer. 


Methyl  violet  5  B 0.025  Sm- 

Neutral  glycerin 30.0      c.c. 

Distilled  water 80.0      c.c. 


After  mixing  the  methyl  violet  and  the  glycerin  add  the  water 
and  to  this  mixture  add  the  following: 


a6 


PRACTICAL  HISTOLOGY 


Sodium  chlorid i .  o  gm. 

Sodium  sulphate 8.0  gms. 

Distilled  water 80. o  c.c. 

After  filtration  the  solution  is  ready  for  use.  As  the  white  cells 
are  stained  violet  they  may  be  counted  at  the  same  time  as  the  red 
cells. 

Hayem's  Solution. 

Bichlorid  of  mercury 0.5  gm. 

Sodium  chlorid 1 .  o  gm. 

Sodium  sulphate 5.0  gms. 

Distilled  water 200 .  o  c.c. 

With  this  solution  only  the  red  cells  are  counted. 
Sherrington's  solution  consists  of  the  following: 

Methylene  blue o .  1 

Sodium  chlorid 1.2 

Neutral  potassium  oxalate 1.2 

Distilled  water 300 .  o 

After  the  blood  has  been  drawn  the  first  drop  is  wiped  away  and 
then  from  the  next  the  blood  is  drawn  up  to  the  mark  1.     The  pipet 

is  then  put  into  the  diluting  fluid 
and  this  is  drawn  up  to  the  mark 
1 01  and  the  contents  of  the  bulb 
thoroughly  mixed.  The  contents 
of  the  stem  of  the  pipette  are  then 
forced  out  and  a  small  drop  of  the 
contents  of  the  bulb  is  then  placed 
upon  the  small  disc  of  the  glass 
m      slide  and  the  cover-glass  applied. 

.  n;||  stage  of  a  microscope  and  then  ex- 
amined  with  a  fifth  inch  (5  mm.), 
or  long  working  distance  one-sixth 
inch  (4  mm.)  objective.  The  red 
cells  in  at  least  25  squares,  but  better  in  100  squares,  are  counted 
and  the  total  number  divided  by  the  number  of  squares  counted. 
This  gives  the  average  content  of  one  square.     This  number  multi- 


Fig.  9. — Neubauer  Ruling. 


TECHNIC 


47 


plied  by  the  cubic  content  of  a  space  (4000)  and  then  by  the  dilution 
(100)  will  give  the  number  of  red  cells  per  cubic  millimeter. 


4000  (cubic  content  y. 

of  one  space)        IO( 


/,.i   ..     %  w  n  (number  of.  cells 
(dilution)  X  counted) 


a  (number  of  squares  counted) 


[  the    number    of 
=  J     red  cells  per 
cu.  mm. 


If  the  white  cells  are  counted  at  the  same  time  their  number  may 
be  got  in  the  same  manner.  If  the  white  cells  alone  are  to  be  exam- 
ined then  the  10  dilution  pipet  is  used  and  the  diluting  fluid  used  is  a 
H  per  cent,  solution  of  acetic  acid.     By  the  use  of  this  the  red  cells 


Fig.  10. — Plan  of  Counting  the  Erythrocytes.     (Da  Costa.) 
The  small  squares  are  examined  in  the  order  indicated  by  the  arrow,  successive 
blocks  of  25  squares  being  covered  until  the  required  number  of  cells  has  been 
counted. 

are  bleached  and  the  white  cells  are  made  more  distinct.  The  same 
counting  method  is  to  be  followed  but  the  dilution  is  only  10,  or 
the  average  number  per  square  may  be  multiplied  by  40,000  instead 
of  by  400,000  as  in  the  case  of  red  cells. 

The  leukocytes  may  be  counted  at  the  same  time  as  the  red  cell 
remembering  that  the  dilution  is  1  to  100. 

In  the  differential  counting  of  leukocytes  at  least  500  white  cells 
should  be  counted.     As  each  cell  is  noted  it  should  be  placed  under 


48  PRACTICAL  HISTOLOGY 

its  proper  class  and  at  the  termination  of  the  count  the  percentage 
of  each  variety  may  be  readily  obtained  by  dividing  its  number  by 
500.  The  count  should  be  made  with  a  Ji2-mcn  oil-immersion 
lens  and  the  slide  should  be  mounted  in  a  mechanical  stage  and 
moved  from  side  to  side.  In  this  manner  the  recounting  of  the 
cells  in  a  given  square  is  avoided. 

Erythroblasts,  if  present,  may  also  be  counted  and  their  number 
per  cubic  millimeter  determined.  The  result  is  only  approximate 
as  it  represents  the  ratio  of  the  nucleated  red  cells  to  a  definite 
number  of  leukocytes.  The  white  cells  are  first  counted,  say  1000, 
and  the  number  per  cubic  millimeter  determined;  then  the  number 
of  nucleated  red  cells  in  the  same  area  is  estimated.  The  number  of 
erythroblasts  per  cubic  millimeter  is  then  determined  by  multiply- 
ing the  number  of  erythroblasts  counted  by  the  number  of  leukocytes 
per  cubic  millimeter  and  dividing  by  the  number  of  leukocytes 
counted  (1000).  It  is  also  usual  to  note  whether  the  red  cells  are 
normoblasts,  or  megaloblasts  and  it  is  necessary  to  determine  the 
ratio  of  these  to  each  other. 

The  blood  platelets  are  also  estimated  indirectly  through  their 
ratio  to  the  erythrocytes.  The  blood  to  be  examined  is  drawn 
directly  into  the  diluting  fluid  (which  is  placed  over  the  puncture). 
This  is  then  thoroughly  mixed  and  some  is  placed  in  the  counting 
chamber  of  the  hemocytometer.  The  number  of  red  cells  per  cubic 
millimeter  is  then  determined  and  a  definite  number  in  a  certain 
area  is  counted.  Then  the  number  of  thrombocytes  in  the  same 
area  is  noted  and  the  ratio  or  number  per  cubic  millimeter  is  gotten 
in  the  same  way  as  that  of  the  nucleated  red  cells  previously  men- 
tioned.    The  average  is  usually  1  platelet  for  each  22  erythrocytes. 

Determann  prefers  the  following  diluting  fluids  for  estimating 
the  number  of  thrombocytes: 

9  per  cent,  aqueous  solution  of  sodium  chlorid,  methyl  violet  sufficient  to 
impart  a  color;  or 

Sodium  chlorid 1  gm. 

Potassium  bichromate 5  gms. 

Distilled  water 100  c.c. 

Methyl  violet  sufficient  to  impart  a  color. 

Toisson's  or  Sherrington's  solutions  may  also  be  used. 


TECHNIC  4Q 

The  estimation  of  the  red  and  white  cells  in  dried  film  preparations 
is  said  to  give  more  accurate  results  than  the  hemocytometer  method. 
The  cells  are  counted  separately  and  tabloid  stains  are  employed; 
that  for  the  leukocytes  consists  of  0.25  gram  of  sodium  chlorid  and 
0.004  gram  of  methyl  violet;  that  for  the  erythrocytes  consists  of 
0.25  gram  of  sodium  chlorid  and  0.0025  gram  of  eosin.  One  of  each 
of  these  tablets  is  dissolved  in  30  c.c.  of  distilled  water  and  0.5 
c.c.  of  formalin  is  added  to  each  and  the  mixtures  are  then  filtered. 

For  counting  the  white  cells  5  cu.  mm.  of  blood  is  drawn  into  a 
graduated  pipet  and  then  mixed  with  495  cu.  mm.  of  the  methyl 
violet  diluting  fluid  (giving  a  dilution  of  1  to  100)  and  thoroughly 
stirred.  Then  5  cu.  mm.  of  this  mixture  are  drawn  into  a  pipet  and 
then  placed  upon  a  slide  so  as  to  cover  an  area  about  10  to  12  mm. 
in  diameter.  This  is  allowed  to  dry  and  then  balsam  and  a  cover- 
glass  are  applied.  The  preparation  is  then  examined  under  a  1.9 
mm.  lens  (using  a  mechanical  stage)  and  all  of  the  leukocytes  in  the 
film  are  counted.  The  number  of  leukocytes  counted  multiplied  by 
20  will  give  the  number  of  leukocytes  per  cubic  millimeter. 

In  estimating  the  erythrocytes  5  cu.  mm.  of  the  above  mixture  for 
examining  the  leukocytes  are  added  to  995  cu.  mm.  of  the  eosin 
mixture;  this  gives  a  dilution  of  1  to  20,000.  After  mixing  and  allow- 
ing the  red  cells  to  stain  for  a  few  minutes  5  cu.  mm.  of  this  mixture 
are  then  placed  upon  a  slide  and  allowed  to  dry  as  previously. 
The  preparation  is  then  covered  with  balsam  and  a  cover-glass  is 
applied.  All  of  the  erythrocytes  in  the  film  are  counted  and  this 
number  multiplied  by  4000,  the  result  is  the  number  of  red  cells  per 
cubic  millimeter. 

The  percentage  of  hemoglobin  in  the  blood  is  determined  by  means 
of  an  hemoglobinometer,  or  hemometer.  There  are  quite  a  few  of 
these  instruments  but  only  Dare'  and  von  Fleischl's  will  be  described 
here. 

The  Dare  hemometer  consists  of  a  'hard  rubber  case  containing 
a  tapering  graduated  semicircle  of  glass  tinted  with  golden  purple  of 
Cassius.  This  is  attached  to  a  disc  and  scale  so  that  the  glass  can 
be  revolved  and  the  scale  read  (from  the  outside).  The  scale  gives 
percentages  from  10  to  120.  A  capillary  blood  chamber  belonging  to 
the  apparatus  consists  of  two  plates  of  polished  glass;  of  these  the 


5° 


PRACTICAL  HISTOLOGY 


one  toward  the  light  consists  of  opaque  glass  while  the  other  is 
transparent.  When  these  two  are  mounted  a  shallow  space  for  the 
blood    exists  between   them.     The    eye-piece  and  tube  cover  two 


Fig.  ii. — Hemoglobinometer  of  Dare. 

R,  milled  wheel;  5,  case  inclosing  the  color 
disc ;  T,  movable  wing,  which  is  swung  out- 
ward; U,  telescoping  camera;  V,  aperture 
admitting  light;  W,  capillary  blood  pipet; 
Y,  detachable  candle  holder;  Z,  slot  through 
which  the  percentage  of  hemoglobin  is  read. 


Fig.  12. — Horizontal  Sec- 
tion of  Dare's  Hemoglobin- 
ometer.     (Da  Costa.) 


Fig.  13. — Method  of  Filling  the  Dare  Blood  Pipet.     (Da  Costa.) 

openings,  one  back  of  the  capillary  chamber  and  the  other  back  of 
the  tinted  graduated  color  standard.  The  section  view  gives  the 
principle  of  the  instrument.  /  represents  the  candle;  0  and  P 
represent  the  two  plates  of  the  capillary  chamber;  L  and  A"  represent 


TECHNIC 


51 


the  color  standard  and  glass  disc;  .1/  and  .1/'  arc  the  openings  com- 
municating with  the  capillary  chamber  and  the  disc  chamber;  N 
is  the  tube  containing  the  eye-piece. 

In  using  the  apparatus  the  capillary  chamber  is  filled  by  touching 
its  edge  to  the  drop  of  drawn  blood  and  then  wiping  the  excess  off. 
It  is  then  placed  in  position  in 
the  apparatus  and  the  candle  is 
lighted.  The  instrument  is  then 
held  to  the  eye  toward  a  dark  wall 
and  the  disc  revolved  until  the 
colors  coincide,  making  sharp 
quick  turns  of  the  milled  wheel. 
The  capillary  chamber  should  be 
taken  apart  and  the  plates  thor- 
oughly cleaned  with  water  and 
acid  alcohol  after  each  use.  J.  C. 
Da  Costa  considers  this  instru- 
ment the  most  accurate,  simple 
and  convenient  for  clinical  pur- 
poses. It  has  the  especial  advantages  of  not  requiring  a  dark 
room  and  of  using  undiluted  blood. 

The  Von  Fleischl  hemometer   consists   of  a  stand  upon  which 
is  mounted  a  movable  wedge-shaped  piece  of  tinted  glass   (golden 

purple  of  Cassius).  Upon  the 
upright  of  the  stand  there  is 
mounted  a  disc  of  plaster  of 
Paris  that  is  used  to  reflect  the 
light  through  the  diluted  blood 
and  color  scale.  In  the  center 
of  the  stage  of  the  stand  there 
is  an  opening  to  accommodate 
the  mixing  chamber.  The  mixing  chamber  is  a  short  cylinder  (with 
a  glass  bottom)  that  is  divided  into  two  compartments  by  a  metal 
partition.  When  properly  mounted  one  compartment  overlies  the 
wedge  of  tinted  glass  and  the  other  contains  the  diluted  blood  and 
receives  the  light  directly  from  the  reflecting  disc.  The  capillary 
pipet  is  of  such  a  capacity  that  one  pipetful  of  normal  blood  diluted 


Fig.   14. — Fleischl's  Hemometer. 
(Da  Costa.) 


Fig.  15. — Colored  Glass  "Wedge  of 
Fleischl's  Hemometer.     (Da  Costa.) 


52 


PRACTICAL   HISTOLOGY 


with  one  compartment  full  of  water  will  give  a  color  that  will  cor- 
respond with  that  of  the  tinted  scale  opposite  the  mark  ioo. 

In  making  the  test  fill  each  compartment 
about  one-quarter  with  distilled  water.  Then 
draw  a  fine  needle  and  thread  through  the 
capillary  pipet  to  clean  it  and  then  apply  the 
pipet  horizontally  to  the  drop  of  blood  drawn 
froim  the  puncture.  Wipe  the  outside  of  the 
pipet  clean  being  careful  that  the  pipet  is  exactly 
full.  Then  wash  the  blood  into  the  compart- 
ment that  is  not  over  the  colored  scale;  this  is 
done  by  the  use  of  a  fine-pointed  pipet  and  the  capillary  pipet 
is  repeatedly  rinsed.  Stir  the  diluted  blood  with  the  handle  of 
the  capillary  pipet  until  evenly  mixed,  rinse  the  handle  into  the 


Fig.  16. — Pipet 
of     Fleischl's 

Hemometer. 


Fig.  17. — Light-proof  Box  for  the  Von  Fleischl  Hemometer.     (Da  Costa.) 
The  door  of  the  box  is  closed  and  the  color  comparison  made  through  the 

camera  tube. 


compartment  and  add  water  cautiously  until  the  compartment  is 
level  full.  Then  fill  the  compartment  over  the  colored  scale  with 
distilled  water  until  exactly  full  taking  care  that  no  water  falls 


TECHNIC  53 

upon  the  thin  partition  as  this  will  cause  a  diffusion  between  the 
two  compartments  and  change  the  result.  If  the  blood  solution  is 
turbid,  due  to  the  presence  of  fat,  a  little  ether  will  clear  it.  The 
instrument  is  then  placed  in  the  lightproof  box,  containing  a  lighted 
candle;  the  lid  is  closed  and  the  operator  then  stands  at  one  end  of 
the  glass  scaled  and  rotates  the  milled  wheel  with  short  ana  rapid 
turns.  The  start  should  be  made  at  the  dark  end  of  the  scale 
and  this  should  be  rapidly  moved  until  the  colors  nearly  coincide. 
After  a  short  rest  the  colors  are  made  to  coincide.  If  the  hemoglobin 
is  30  per  cent,  or  under  it  is  best  to  use  two  or  three  pipets  of  blood 
and  then  divide  the  result  by  two  or  three  as  the  case  may  be. 
It  is  said  that  with  the  best  of  care  an  error  of  50  may  occur  on 
account  of  the  large  field  of  the  mixing  chamber.  To  obviate  this 
a  mental  diaphragm  with  a  slit  about  one-eighth  of  an  inch  in  width 
is  placed  under  the  glass  bottom  of  the  mixing  chamber  so  that  the 
slit  is  at  a  right  angle  to  the  partition.  This  cuts  down  the  field  to 
about  2. 50  of  the  glass  scale  and  thus  greatly  reduces  the  error. 

Slide  Technic. — The  preparation  of  sections  for  microscopic 
study  requires  skill  and  care. 

Paraffin  sections  are  made  to  adhere  to  the  slide  by  means  of 
Mayer's  albumen.  This  is  prepared  by  mixing  thoroughly  white 
of  egg  and  glycerin  in  equal  parts  and  filtering.  To  the  nitrate  add 
1  gram  of  sodium  salicylate.     A  very  thin  film  is  all  that  is  necessary. 

The  following  desk  reagents  are  sufficient  for  all  ordinary  work : 

Coplin  staining  jar,  containing  Iodin. 

Coplin  staining  jar,  containing  Kerosene,  or  Xylol. 

Coplin  staining  jars,  containing  Alcohol.     Nos.  1  and  2. 

One  Barnes  bottle,  containing  Hematoxylin. 

One  Barnes  bottle,  containing  van  Gieson's  stain. 

One  Barnes  bottle,  containing  Eosin. 

One  Barnes  bottle,  containing  Alcohol. 

One  Barnes  bottle,  containing  Water. 

One  Barnes  bottle,  containing  Acid  Alcohol. 

One  Barnes  bottle,  containing  Creosote. 

One  Barnes  bottle,  containing  Albumen. 

One  Barnes  bottle,  containing  Picric  Acid, 


54  PEACTICAL  HISTOLOGY 

The  method  of  procedure  for  staining  is  given  in  detail  below: 
i.  Cover  a  clean  slide  with  a  thin  film  of  albumen. 

2.  Add  a  few  drops  of  water,  and  upon  this  float  the  cut  paraffin 
section. 

3.  Warm  gently  over  a  flame,  so  as  to  spread  the  section,  but  be 
careful  not  to  melt  the  paraffin. 

4.  Drain  and  set  aside,  or  in  an  oven,  for  six  to  twenty-four  hours. 
The  slide  must  be  perfectly  dry  before  the  other  steps  can  be  carried 
out.     Put  an  identification  label  on  the  slide. 

5.  Place  in  the  kerosene  for  five  to  fifteen  minutes,  to  remove  the 
paraffin.     Xylol  may  be  used. 

6.  Wash  with  alcohol,  to  remove  the  kerosene,  and  place  in  the 
jar  of  iodin,  five  to  ten  minutes,  to  remove  the  crystals  of  bichlorid  of 
the  fixing  agent. 

7.  Remove  the  excess  iodin  from  the  slide  with  tissue  paper, 
wash  with  alcohol  and  place  in  the^r^  alcohol  jar  for  fifteen  minutes, 
to  remove  the  remainder  of  the  iodin.  This  may  be  hastened  by 
the  addition  of  a  little  potassium  iodid  to  the  alcohol. 

If  a  bichlorid  fixative  has  not  been  used  steps  6  and  7  may  be 
omitted. 

8.  Drain  the  section,  wash  with  water,  cover  with  hematoxylin 
for  three  to  five  minutes,  and  wash  with  water  to  deepen  the  color. 

9.  Counter-stain. — Eosin  one  to  two  minutes,  wash  with  water 
to  remove  excess  stain  and  then  alcohol;  or, 

Van  Gieson  one  to  one  and  one-half  minutes,  wash  with  water 
and  then  alcohol,  as  above;  or, 

Picric  acid  fifteen  seconds  and  wash  with  alcohol. 

Carmin  may  be  used  alone  for  fifteen  minutes,  or  followed  by 
picric  acid,  as  in  the  preceding.  If  carmin  is  used  alone  wash  the 
excess  off  with  water  and  then  cover  with  acid  alcohol  to  differentiate. 
When  the  color  becomes  a  brick-red,  wash  the  acid  alcohol  off 
quickly  with  ordinary  95  per  cent,  alcohol  and  dehydrate  in  the  usual 
way.     Hold  the  slide  in  the  hand  while  differentiating. 

10.  After  washing  with  alcohol,  dehydrate  in  the  second  jar  of 
alcohol.     Allow  sections  to  remain  about  five  minutes. 

11.  Clean  the  slide  carefully  without  allowing  the  section  to  dry. 
Blot  with  tissue-paper. 


TECHNIC  55 

12.  Cover  with  a  drop  or  two  of  creosote  for  five  minutes.  This 
removes  the  alcohol,  renders  the  specimen  transparent,  and  allows 
the  use  of  balsam.     This  is  section  clearing. 

13.  Drain  off  the  creosote,  blot,  add  a  drop  of  balsam  and  cover 
with  a  clean  cover-glass. 

14.  Remove  the  identification  label,  apply  a  clean  one,  and  write 
the  name  of  the  section  thereon. 

After  the  paraffin  has  been  removed,  the  specimen  should  never 
be  allowed  to  dry. 

The  above  technic  will  answer  for  all  ordinary  histologic  and 
pathologic  work,  and,  if  strictly  adhered  to,  there  will  not  be  the 
slightest  trouble  in  making  excellent  preparations. 


CHAPTER  II 
THE  CELL  AND  ITS  PROPERTIES 

Histology  is  the  science  that  treats  of  the  minute  structure  of 
normal  tissues  and  organs.  Although  to  the  naked  eye  tissues  may 
have  an  apparent  structure  that  seems  ultimate,  when  examined 
under  the  microscope  this  structure  is  seen  to  be  but  gross.  Each 
section  studied  will  be  found  to  be  composed  of  minute  elements, 
more  or  less  regular,  and  definitely  grouped  and  arranged.  These 
elements  are  cells. 

Protoplasm  is  a  viscid  substance  of  neutral  reaction  and  is  es- 
sentially a  colloidal  substance.  It  consists,  chemically,  of  (a) 
water  that  constitutes  two-thirds  of  its  weight;  (b)  inorganic  sub- 
stances as  salts  of  calcium,  potassium,  sodium,  chlorin,  phos- 
phorus and  oxygen  (free  or  in  combination);  (c)  organic  salts  of 
usually  phosphorus  and  iron,  in  the  form  of  proteins  and  nucleo- 
proteins.  In  addition  certain  nonprotein  substances  as  lecithin 
and  cholesterin  are  essential  components  of  protoplasm. 

Physically  the  cytoplasm  consists  of  colloids  and  crystalloids  held 
in  suspension  by  the  water.  The  colloids  are  present  in  two  con- 
ditions (i)  liquid  or  sol  and  (2)  semi-solid  or  gel.  The  crystalloids 
are  (1)  electrolytes  (bases,  acids  and  salts)  and,  (2)  nonelectrolytes 
(urea,  sugar).  There  is  no  sharp  line  between  colloids  and  crys- 
talloids. As  the  fluidity  of  protoplasm  is  due  to  water  and  as  pro- 
toplasm is  sol  it  is  usually  called  hydrosol.  When,  however,  it  is 
converted  into  the  semi-solid  or  gel  state  it  is  referred  to  as  hydrogel. 
This  changing  from  the  one  to  the  other  is  constantly  going  on  in 
the  living  cells  and  should  an  irreversible  hydrogel  be  formed  then 
life  tends  to  cease. 

Living  protoplasm  in  structure  is  a  granular  gel.  Kite  con- 
siders it  an  emulsoid  of  which  the  colloidal  particles  are  the  struc- 
tural units.     It  is  a  viscous  hydrogel,  apparently  homogeneous,  in 

56 


III!'.    CELL 


57 


which  are  granules  of  denser  gels  and  liquid  globules.     Spindle  libers 
seem  to  be  definite  and  distinct  comparatively  rigid  threads.     The 


Fig.  18. — Microscope  Suitable  for  General  Work. 
a.  Ocular  or  eye-piece;  b,  draw-tube;  c,  rack;  d,  milled  head  of  pinion  mov- 
ing the  rack;  the  rack  and  pinion  (c  and  d)  together  are  called  the  coarse 
adjustment;  e,  microscopic  tube;  /,  micrometer  screw  by  which  the  fine 
adjustment  is  operated;  g,  triple  nose-piece  or  revolver  which  receives  the 
objectives,  h;  in  the  above  instrument  there  are  three  objectives  which  in 
turn  may  be  rotated  into  the  optical  axis;  i,  stage  on  the  upper  surface  of 
which  are  clips  for  holding  the  slide  during  examination;  j,  iris  diaphragm 
in  substage  condenser;  the  diaphragm  permits  variation  in  the  quantity  of 
light  admitted,  and  the  condenser  properly  focuses  the  rays  on  the  object 
examined;  k,  screw  for  raising  and  lowering  the  condenser  by  which  the 
latter,  when  not  in  use,  may  be  thrown  to  the  side;  /,  mirror  for  reflecting 
light  into  the  optical  axis  of  the  intrument;  m,  inclination  joint  permitting 
inclination  of  the  instrument.  The  vertical  column  below  the  inclination 
joint  is  called  the  pillar  and  is  solidly  joined  to  the  large,  heavy,  horseshoe 
base  supporting  the  instrument. 

nuclear  granules  and  network  he  regards  as  denser  masses  of  nuclear 
gel  that  gradually  grade  into  the  diluter  gel  of  the  achromatin. 


58 


PRACTICAL  HISTOLOGY 


A  cell  is  a  small  mass  of  protoplasm  containing  a  nucleus.  It  is 
the  histologic  basis  of  the  body,  and  has  a  complex  structure. 
Certain  parts  are  absolutely  essential  for  the  proper  peformance  of 
its  various  functions,  while  others  are  accessories,  which  most  cells 
possess.     The  parts  of  a  typic  cell  are: 

i.  Cell-body. 

2.  Nucleus.  - 

3.  Centrosome. 

4.  Nucleolus. 

5.  Cell-wall. 


Fig.    19. — Scheme    of    a    Cell. — Microsomes    and    spongioplasm  only  partly- 
sketched.     (Stohr's  Histology.) 

1,  Spongioplasm;  2,  hyaloplasm;  3,  microsomes;  4,  exoplasm;  5,  chromatin; 
6,  achromatin;  7,  linin;  8,  chromatic  knots;  9,  nuclear  membranes;  10, 
centrosome;  11,  nucleolus;  12,  cell-membrane;  13,  inclusions. 

i.  The  cytoplasm  or  cell-body,  may  or  may  not  be  limited  by  a 
cell-wall  and,  in  fixed  cells,  it  consists  of  two  main  parts,  the  spon- 
gioplasm, or  filar  mass  and  the  hyaloplasm,  or  inter  filar  mass. 

The  spongioplasm,  as  its  name  indicates,  is  a  framework  of  com- 
paratively solid  structure,  in  the  meshes  of  which  is  found  the  semi- 


THE    CELL 


59 


fluid  hyaloplasm  or  paraplasm.     The  elasticity  of  the  spongioplasm 
is  said  to  give  rise  to  ameboid  movements. 

In  the  cytoplasm  are  to  be  seen  small  darkly  staining  bodies, 
the  microsomes  and  paler  masses,  the  plastids.     At  the  outer  margin 


Fig.  20. — Fat  Globules  in  the  Cells  of  the  Zona  Glomerulosa  of  the 
Adrenal  Gland  Fixed  in  Osmic  Acid.     (Photograph.  Obj.  16  mm.,  oc.  10  X.) 


Fig.  21. — A  Section  of  an  Acinus  of  the  Pancreas  of  a  Guinea-pig. 

The  zymogen  granules  are  in  the  lumen  end  of  the  cell  while  the  mitochondria 
are  basally  disposed.     (After  Bensley.) 


of  the  cell-body  is  a  narrow,  peripheral  zone,  containing  no  micro- 
somes, known  as  exoplasm.  At  times  there  are  other  structures  pres- 
ent, as  fat  globules,  glycogen,  secretion  granules,  vacuoles,  pigment, 


6o 


PRACTICAL   HISTOLOGY 


crystals,  waste  products,  as  creatin,  creatinin,  urea,  urates,  etc.     These 
nonprotein  substances  constitute  paraplasm. 

The  granules  may  be  diffusely  scattered  or  collected  into  groups 
and  are  probably  formed  under  the  influence  of  the  nucleus.  These 
vary  in  size  and  number  in  the  same  cell  and  different  cells.  They  may 
be  almost  ultramicroscopic  or  large  as  seen  in  nerve  cells  (tigroid 
bodies).     In  glandular  cells  they  can  be  seen  gradually  increasing 

in  size  as  the  elaboration  of  the 
secretion,  with  which  they  are 
connected,  is  progressing.  They 
respond  to  different  stains  in  the 
different  cells;  some  granules  are 
eosinophilic,  others  basophilic  and 
still  others  neutrophilic.  This  is 
especially  distinct  in  the  different 
types  of  leukocytes.  As  regards 
the  functions  of  granules  some  are 
secretory,  as  in  glandular  cells, 
and  others  are  nutritive,  as  in 
nerve  cells.  These  granules  seem 
to  be  formed  under  the  influence  of  the  nucleus. 

Some  granules  seem  to  form  contractile  fibrils,  which  stain  dis- 
tinctly and  are  called  mitochondria;  these  fibrils  sometimes  form 
spherical  masses  called  chondromitomes.  Mitochondria  seem  to  be 
related  to  the  metabolic  activities  of  the  cell,  the  formation  of 
presecretion  and  excretion  granules  and  the  formation  of  fibrillar 
in  muscle  fibers.  Meves  believes  that  the  mitochondria  share  with 
the  chromosomes  the  transmission  of  hereditary  characters  and  others 
that  they  represent  the  region  of  and  assist  in  oxidation  processes. 
In  the  germ  cells  the  mitochondria  are  of  a  granular  form  while  in  the 
somatic  cells  they  are  filaments  or  rods.  They  are  found  in  all 
types  of  cells,  in  living  plant  cells  and  in  animal  cells  grown  in 
artificial  media.  In  the  latter  instance  they  were  studied  by  W.  H. 
and  M.  R.  Lewis  who  found  that  they  changed  shape,  divided  into 
granules  and  reunited  into  filaments.  In  fixed  material  they  seem  to 
be  lipoid  precipitation  products  having  a  chemical  composition  of 
lipoid  (phosphatid). 


Fig.  22. — Interstitial  Cells  of 
the  Human  Testis  Showing 
Mitochondria  of  the  Gran- 
ular and  Filamentous  Forms. 
{After  Winniivarter.) 


THE    CELL 


6l 


In  many  nerve  and  glandular  cells  (stomach,  liver;  is  seen  a  fine 
network  of  anastomosing  channels,  or  secretory  capillaries,  called 
trophospongium.  These  are  supposed  to  be  connected  with  the 
circulation  of  nutritive  material  or  secretion  products.  These  may 
conduct  the  secretion  to  the  ducts,  or  to  the  lymph  or  blood-vessels. 
In  the  two  latter  instances  the  secretion  would  be  called  internal. 
Holmgren  believes  that  these  channels  have  definite  openings  upon 
the  surface  of  the  cell  while  v.  Bergen  states  that  these  canaliculi 
are  not  permanent  but  come  and  go. 


Fig.  23. — Intestinal  Cells  of  the  Rain- 
bow Trout  Showing  Mitochondria. 
{After  Jordan  and  Ferguson.) 


Fig.  24. — Intracellular  Canal- 
iculi.    {After  Holmgren.) 


Fibrils  are  noted  in  various  cells.  In  nerve  cells  they  form  a  net- 
work and  are  called  neurofibrils;  in  muscle  cells  they  are  parallel  to 
one  another  and  are  the  muscle  fibrillce. 

The  cell-body  has  affinity  for  acid,  or  protoplasmic,  stains,  such  as 
eosin,  picric  acid,  carmin,  orange,  etc. 

2.  The  nucleus  is  usually  a  darkly  staining,  refractile  body  having 
a  sharp  outline,  and  occupying,  as  a  rule,  a  central  position.  It 
controls  metabolic  activities  and  in  cell  division  transmits  character- 
istic features  (heredity).  In  glandular  cell,  its  location  varies  with 
the  stage  of  secretory  activity.  Its  structure  resembles  that  of 
the  cytoplasm,  to  a  certain  extent.  The  nucleus  consists  of  a 
network  and  semi-fluid  substance,  surrounded  by  a  distinct  mem- 
brane or  wall.  The  network  is  called  the  chromatin,  or  nuclear 
fibrils,  and  the  semi-solid  substance,  the  nuclear  matrix,  sap 
or  achromatin. 


62 


PRACTICAL  HISTOLOGY 


Chromatin  or  karyotome  is  the  part  of  the  nucleus  that  responds 
to  the  stains.  It  is  arranged  as  an  irregular  network  of  anastomos- 
ing fibrils,  each  consisting  of  a  delicate  central  thread,  the  linin, 
upon  which  the  real  chromatin  substance  is  arranged,  in  the  form 
of  granules  {chromioles).  Where  the  chromatin  threads  cross  each 
other  large  masses  of  chromatin  at  times  are  seen;  these  are  called 
karyosomes.     It  is  the  most  important  portion  of  the  nucleus  during 

the  process  of  cell-division.  In 
glandular  cells  the  chromatin 
increases  during  the  earlier 
stages  of  secretory  activity  and 
decreases  during  the  later 
stages.  The  diminution  prob- 
ably represents  the  formation 
of  special  secretion  products. 
During  cell  division  the  chro- 
matin separates  into  a  number 
of  rod-like  structures  {chromo- 
somes) that  are  of  the  same  size 
and  constant  in  number  for  the 
same  species  of  animal,  in  each 
nucleus.  Each  chromosome 
consists  of  chromioles  and  both  are  capable  of  growth  and  of  multi- 
plication by  division. 

Chromatin  consists  of  nucleic  acid  combined  with  protein  and 
has  an  affinity  for  basichromatic  stains.  The  linin  is  mucoid  in 
nature,  contractile  and  oxyphilic  in  reaction. 

The  achromatin  or  karyoplasm  is  a  semi-fluid  substance  that  fills 
in  the  meshes  of  the  chromatin.  In  the  living  condition  it  is  appar- 
ently structureless  but  when  fixed  and  stained  it  exhibits  little 
granules  that  respond  to  the  plasmatic  dyes,  called  oxy  chromioles. 

The  nuclear  membrane  is  that  wall  that  sharply  outlines  the 
nucleus.  It  is  present  in  all  nuclei  and  is  solid.  Upon  its  inner 
surface  it  is  connected  with  the  chromatin  network.  It  consists 
of  amphipyrenin  (basichromatin  and  linin)  and  responds  to  basi- 
chromatic dyes. 

Of  the  above  structures,  the  chromatin  persists  throughout  all 


Fig.  25. — Intracellular  Canaliculi  of 
the  Liver  Cells  Communicating 
with  the  Sinusoids.    {After  Schdfer.) 


THE    CELL 


63 


the   stages   of   reproduction,    while   the   remainder   of    the   nuclear 
constituents  disappear. 

The  nucleus  responds  to  nuclear  stains  as  hematoxylin  and  basic 
a  nil  in  dyes. 

3.  The  centrosome  is  a  small  darkly  staining  structure,  which, 
owing  to  its  small  size,  has  been  found  in  but  few  of  the  cells  of  the 
human  body.  It  is  readily  seen  and  studied  in  the  ova  of  some  of 
the  lower  animals,  especially  those  of  ascaris  megalocephala.  It 
lies,  usually,  just  outside  of  the  nucleus, 
in  a  small  clear  field  called  the  attraction 
sphere,  within  which  are  seen  delicate 
lines  that  radiate  from  the  centrosome. 
The  attraction  sphere  and  the  centro- 
some constitute  the  astrosphere,  usually 
less  than  i/z  in  diameter.  In  many 
gland  cells  the  centrosome  lies  where  the 
secretion  accumulates.  In  intestinal 
epithelium  that  sends  out  pseudopodia 
it  lies  at  the  point  of  origin  of  these 
processes.  It  is  occasionally  divided 
constituting    then    a    diplosome.      In 

cells  possessing  multiple  or  lobulated  nuclei  the  centriole  usually 
consists  of  a  group  of  particles  (giant-cells  of  bone-marrow). 

Besides  starting  cell -division,  the  centrosome  seems  to  play  an 
important  part  during  the  resting  stage.  In  pigment  cells  and 
white  blood-corpuscles,  it  seems  to  preside  over  the  movements 
of  the  whole  cell,  and  in  ciliated  and  flagellated  cells  over  the  action 
of  these  processes.     It  responds  to  the  iron-hematoxylin  stain. 

4.  The  nucleolus  or  plasmosome  is  a  small,  oxyphilic  body  found 
within  the  nucleus.  It  is  not  always  present,  and  more  than  one 
may  be  found.  In  nerve  cells  and  ova  it  is  unusually  large  and 
readily  stained,  while  in  others  it  is  scarcely  noticeable.  It  is  prob- 
ably the  result  of  nuclear  activity  and  at  times  parts  of  the  nucleoli 
are  passed  into  the  cytoplasm.  Some  say  that  these  particles  are 
formed  into  secretion  granules  and  others  claim  that  they  represent 
effete  material.  Its  importance  is  doubtful,  although  it  is  now  be- 
lieved to  be  concerned  in  the  formation  of  the  central  spindle  during 


Fig.  26. — Trophospongium 
within  a  Ganglion  Cell. 
{After  Holmgren.) 


64  PRACTICAL   HISTOLOGY 

cell-division.  It  consists  of  pyrenin,  disappears  during  cell-division 
and  is  considered  by  some  the  seat  of  basichromatin  formation. 
This  is  utilized  by  the  chromosomes. 

5.  The  cell -wall  is  a  more  or  less  prominent  membrane  that  limits 
cells.  It  is  not  present  in  all  animal  cells,  though  all  cells  possess 
a  delicate  membrane  that  is  solid  and  of  a  lipoid  nature.  In  some 
instances,  it  consists  of  the  differentiated,  peripheral  cytoplasm, 
and  in  others,  is  a  secretory  product  of  the  cytoplasm.  When  a 
well-defined  wall  surrounds  the  entire  cell  it  is  called  a  pellicula 
(seldom  used);  if  it  is  found  upon  the  exposed  surface,  as  in  the 
intestinal  cells,  it  is  termed  a  caticular  border. 

Of  the  above  structures,  the  cytoplasm,  nucleus  and  centrosome 
are  the  essential  parts,  when  the  important  functions  of  the  cell  are 
considered.  In  red  blood-cells  the  nucleus  is  absent,  and,  as  a  con- 
sequence, these  cells  cannot  reproduce  themselves. 

Cells  differ  greatly  in  form  and  size  from  4/x  to  8oju;  the  nucleus 
conforms  somewhat  to  the  shape  of  the  cell.  The  lobulated  nucleus 
of  the  leukocyte  is  a  peculiar  modification  of  this  general  rule. 
Usually  but  one  nucleus  is  present,  but  in  giant  cells  and  voluntary 
striated  muscle,  many  are  to  be  found. 

Cells  may  fuse  so  as  to  form  a  single  mass  of  protoplasm  with 
nuclei  at  fairly  regular  intervals.  This  is  called  a  syncytium.  This 
term  has  also  been  applied  to  striated  muscle  tissue  on  account  of  the 
large  number  of  nuclei  present. 

The  cell,  like  the  organism,  exhibits  a  number  of  properties,  such 
as  metabolism,  growth,  motion,  irritability  and  reproduction. 

Metabolism  is  the  sum  of  all  of  the  changes  that  take  place  in  a 
cell  during  the  performance  of  its  functions.  The  metabolic  proc- 
esses are  controlled  by  the  nucleus.  The  changes  are  chemical  in 
nature  and  are  increased  by  warmth  and  electrical  stimuli.  When 
the  result  is  the  formation  of  complex  structures,  the  process  is 
called  anabolism;  if  destructive,  the  conversion  of  complex  to  simple 
compounds,  the  phenomenon  is  termed  katabolism.  Secretion  and 
excretion  are  anabolic  changes,  as  simple  structures  are  converted 
into  complex  compounds.  Secretion  may  be  glandular  secretion, 
or  simply  an  intercellular  substance  may  be  formed. 

Growth  is  the  result  of  an  anabolic  process.     The  cells  increase 


MOTION  65 

in  size,  equally  or  more  often  unequally,  depending  upon  the  organ. 
When  the  latter  occurs,  the  cell-form  is  changed.  By  such  a  change 
in  all  cells,  the  organism  increases  in  size,  though  the  amount  con- 
tributed by  each  cell  may  be  microscopic. 

Motion. — Cells  exhibit  the  phenomenon  of  movement  under  three 
forms:  protoplasmic,  ameboid  and  ciliary. 

Protoplasmic  movement  is  difficult  of  observation  on  account  of 
the  slowness  of  the  process.  It  has  been  demonstrated  in  a  few 
animal  cells  but  in  plant  cells  it  is  easily  observed,  the  streaming 
of  the  cytoplasm  being  an  example  (cyclosis).  All  animal  cells  are 
believed  to  possess  it  to  a  greater  or  lesser  degree.  It  is  made 
manifest  by  the  changes  in  the  form  of  the  cytoplasm,  by  move- 
ments of  the  microsomes  and  by  the  changes  in  the  position  of  the 
nucleus. 

Ameboid  movement  is  similar  to  that  exhibited  by  the  unicel- 
lular animal,  the  ameba.  Nearly  all  animal  cells  possess  it  to  some 
extent,  it  being  well  marked  in  especially  a  few  cells,  viz.,  the 
leukocytes,  lymph  cells  and  wandering  connective-tissue  cells.  If 
a  living  leukocyte  be  studied  under  the  microscope  it  will  be  seen 
to  change  continually  in  form.  Gradually  a  bud-like  process  of  the 
protoplasm  will  push  out  from  one  point  or  several  may  start  from 
different  points.  These  pseudopodia  may  retract  or  be  extended  for 
a  considerable  distance,  the  remainder  of  the  cytoplasm  flowing  into 
one.  Other  pseudopodia  are  given  off  and  the  process  is  repeated. 
These  processes  may  be  either  massive  or  lobed,  or  fine  and  spine-like. 
By  this  means  the  cell  will  gradually  crawl  across  the  field  of  the 
microscope.  It  is  by  means  of  this  ameboid  movement  that 
leukocytes  pass  through  the  walls  of  the  capillaries  (diapedesis) 
and  wander  through  the  spaces  of  the  tissues  and  organs  or  between 
other  cells.  This  phenomenon  is  also  exhibited  when  an  ameboid 
cell  takes  in  foreign  particles,  i.e.,  ingestion  of  food,  or  when 
phagocytes  attack  bacteria  or  tissues. 

Ciliary  motion  is  limited  to  only  a  portion  of  the  cell,  that  is,  to 
delicate  hair-like  processes  called  cilia.  In  true  ciliated  cells  it  is 
said  that  a  darkly  staining  body  (presumably  centrosomic  in  origin) 
is  to  be  found  at  the  central  end  of  each  cilium.  The  spermium 
moves  by  the  action  of  its  tail,  a  flagelloid  structure. 


66  PRACTICAL  HISTOLOGY 

One  of  the  most  characteristic  examples  of  motion  is  exhibited  by 
the  muscles,  especially  the  voluntary  striated  variety;  here  although 
the  whole  cell  moves,  the  motion  is  limited  to  one  direction.  This 
is  parallel  to  the  long  axis  of  the  fibers  and  constitutes  contraction. 

Irritability  is  the  property  that  cells  have  of  responding  to  external 
stimuli.  This  property  is  exhibited  best  in  the  unicellular  animals 
and  others  that  possess  no  nerve  system.  In  these  forms  it  is  a 
primary  change  in  the  cell.  These  stimuli,  although  almost  in- 
numerable, may,  in  a  general  manner,  be  grouped  as  mechanical, 
electrical  and  chemical  in  their  nature,  or  due  to  heat  or  light. 

All  cells  do  not  respond  in  the  same  manner  to  the  same  stimulus, 
nor  do  all  stimuli  cause  the  same  reaction  in  an  individual  cell.  The 
response  of  a  cell  to  a  specific  stimulus  depends  upon  its  structure. 
Some,  those  of  the  organ  of  vision  for  example,  respond  to  light  only, 
while  others  may  respond  to  one  or  more  stimuli. 

Under  mechanical  stimuli  are  pressure,  violent  shaking  and  crush- 
ing, any  one  of  which  will  cause  cells  to  respond  in  some  manner. 

While  heat  is  a  necessary  condition  for  the  activities  of  a  cell  it 
must  be  confined  within  rather  fixed  limits,  these  varying  consider- 
ably, however,  for  different  cells.  If  the  temperature  be  raised  to 
4o°C.  (io4°F.)  the  vitality  of  the  cell  is  destroyed;  upon  the  other 
hand  the  temperature  may  be  lowered  to  a  considerable  extent 
without  the  cell  being  killed.  An  increase  of  heat  above  that  at 
which  the  cell  normally  exists  causes  a  marked  increase  in  its  vital 
processes  until  the  heat  rigor  point  (4o°C.)  is  reached  when  a  coagula- 
tion takes  place  and  the  cell  is  killed.  Lowering  of  the  temperature 
below  the  normal  produces  a  gradual  lessening  of  activity  until  cold 
rigor  (o°C.)  point  is  reached  when  the  cell  passes  into  a  narcotic  state. 
Apparently  cells  may  remain  in  this  state  for  a  considerable  length 
of  time  without  their  vitality  being  destroyed,  for  if  they  be  gradu- 
ally warmed  up  to  their  normal  temperature  their  vital  functions 
are  resumed. 

Light,  in  the  higher  order  of  animals,  is  supposed  to  be  a  stimulus 
to  the  organs  of  vision  only.  In  some  of  the  lower  animals  other 
tissue  cells,  especially  those  of  the  skin,  respond  to  its  stimulation. 

Electrical  stimuli,  when  applied  in  the  form  of  weak  currents,  cause 
an  increase,  strong  currents  a  decrease,  in  cell  activity.     If  the  latter 


REPRODUCTION 


67 


are  continued  for  a  considerable  time  they  will  cause  the  death  of  the 
cell. 

Chemical  stimuli  are  almost  numberless  and  at  present  their  action 
is  not  thoroughly  understood.  Some  cause  contraction,  some  in- 
creased movements  and  others  increased  secretory  activity,  etc.  A 
striking  feature  of  the  unilateral  action  of  chemical  stimuli  is  that 
known  as  chemotaxis.  This  is  the  property  possessed  by  certain  cells 
of  responding  to  the  stimulation  of  chemical  substances  introduced 
into,  or  formed  in  the  body.  Some  substances  cause  cells  to  ap- 
proach them  {positive  chemotaxis)',  others  repel  them  {negative 
chemotaxis).  The  leukocytes  respond  quickly  to  this  form  of 
stimulation.  Such  movements  may  be  produced  by  the  addition  or 
subtraction  of  water,  producing  relaxation  and  contraction,  re- 
spectively. Chemical  action  is  also  dependent  upon  the  concen- 
tration of  the  salts  and  upon  the  contained  electrolytes.  Chemotaxis 
plays  a  very  important  part  in  many  physiological  phenomena,  as  for 
example,  the  tendency  to  seek  oxygen,  the  attraction  of  leuko- 
cytes toward^  bacterial  activity  and  the  attraction  exerted  by  the 
ovum  upon  the  spermium. 

Reproduction  is  the  process  by 
means  of  which  a  cell  or  an  organism 
propagates  itself  and  continues  its 
life  history.  Without  this  or  an 
analogous  process,  life  would  soon 
cease  to  exist.  It  is  of  two  varieties, 
direct,  amitosis  or  budding  and  in- 
direct, mitosis  or  karyokinesis.  Of 
these,  the  latter  is  the  more  common. 

Amitosis. — This  form  of  cell  division  was  formerly  thought  to  be 
the  usual  method,  but  it  is  now  known  to  be  restricted  to  some  cells 
of  the  bladder,  cells  of  Sertoli  of  the  testis,  giant  cells  of  the  bone- 
marrow  and  occasionally  to  leukocytes  and  gland  cells.  By  some 
it  is  considered  a  sign  of  degeneration.  The  nucleus  in  this  form 
of  cell  division  divides  without  the  intranuclear  network  undergoing 
the  same  complicated  changes  as  in  the  indirect  method. 

The  nucleus  .first  becomes  constricted;  this  constriction  gradually 
increases  and  finally  divides  the  nucleus  into  two  equal  parts  forming 


Fig.   27. — Amitosis  of  a  Cell  of 
the  Bladder.      (After  Xemileff.) 


68 


PRACTICAL  HISTOLOGY 


daughter  nuclei;  these  daughter  nuclei  draw  away  from  each  other 
by  ameboid  movement.  At  times  the  complete  division  is  delayed 
and  the  two  nuclei  are  connected,  for  some  time,  by  a  narrow  thread 
of  nuclear  material.  Division  of  the  cytoplasm  takes  place  by  the 
development,  at  first,  of  a  constriction  in  that  portion  of  the  cell 
body  between  the  nuclei  and  then  finally  by  the  entire  separation  of 
the  daughter  cells  thus  formed.  Like  the  nucleus  the  cytoplasm 
may,  in  some  instances,  remain  connected,  or  its  division  may  be 
delayed  while  the  nuclei  go  on  dividing,  the  result  being  an  ac- 
cumulation of  nuclei  and  the  formation  of  a  multinucleated  cell. 


Central  spindle. 


Chromosomes. 


Centrosomes. 


Wf 


Fig.  28. — Scheme  of  the  Close  Skein 
and  the  Division  of  the  Centro- 
somes.     (Stohr's  Histology.) 


Fig.  29. — Scheme  of  the  Loose  Skein 
and  Separation  of  the  Centro- 
somes.    (Stohr's  Histology.) 


Mitosis  is  a  very  complex  process,  in  which  the  nucleus  plays  a 
very  important  part.  The  cytoplasm  is  almost  passive  until  the 
late  stages  of  the  process.  The  various  stages  are  the  prophase, 
metaphase,  anaphase,  and  telophase.  These  are  not  absolutely 
separable  from  one  another.  The  changes  that  occur  may  be  grouped 
under  three  heads — nuclear,  centrosomic  and  cytoplasmic. 

Prophase. — The  nuclear  changes  are  quite  complex.  Whereas 
the  chromatin  is  ordinarily  arranged  as  an  irregular  network,  when 
division  begins  the  irregular  twigs  of  the  network  gradually  become 
smooth,  and  form,  usually,  a  single  thin  closely  convoluted  thread, 
called  the  spirem,  or  skein.  This  thread  consists  of  a  double  row 
of  chromatin  granules  (chromioles).     The  thread  becomes  thicker 


REPRODUCTION  69 

and  shorter,  and  soon  separates  into  a  number  of  segments  called 
chromosomes.  This  sometimes  occurs  before  the  spirem  is 
formed.  The  chromosomes  become  U-  or  V-shaped,  and  arrange 
themselves  along  the  equator  of  the  cell  with  the  closed  ends  directed 
toward  a  common  center,  called  the  polar  field.  This  arrangement  is 
termed  the  equatorial  plate,  or  monaster,  and  practically  ends  the 
chromatin  changes  during  the  prophase.  The  chromosomes  vary 
from  two  to  sixty-four  in  different  species. 

Polar  radiation.         Nuclear  spindle. 


Fig.    30. — Scheme   of   the    Mother       Fig.  31. — Scheme  of    Metakinesis, 
Star,    or     Equatorial      Plate.  Showing    the  "Nuclear  Spindle. 

(Slohr's  Histology.)  (Stohr's  Histology.) 

The  chromosomes  are  always  even  in  number,  and  the  same 
number  is  always  formed  in  each  cell  of  the  same  species.  In  man, 
the  number  is  said  to  be  twenty-four. 

The  nuclear  membrane,  during  these  changes,  has  gradually  be- 
come more  and  more  hazy,  and  finally  disappears.  The  achromatin 
is  released,  and  mixes  with  the  cytolymph. 

The  nucleolus  likewise  gradually  fades  and  disappears  to  assist  in 
the  formation  of  the  central  spindle  (Ferguson). 

The  centrosome  is  the  dynamic  center  of  the  cell.  It  divides 
into  two  portions  (if  within  the  nucleus,  it  passes  first  into  the 
cytoplasm),  each  of  which  becomes  surrounded  by  its  own  attraction 
sphere.  These  centrosomes  gradually  move  apart,  through  an  arc 
of  oo°,  to  opposite  poles  of  the  cell.  During  this  change,  some  of  the 
intervening  rays  remain  in  contact,  forming  a  spindle  of  delicate 
threads,  which  is  complete  when  the  centrosomes  reach  their  polar 


7<D  PRACTICAL  HISTOLOGY 

position.  This  is  the  central,  or  achromatic  spindle,  and  the  threads 
are  of  the  utmost  importance,  and  become  attached  to  the  chro- 
mosomes of  the  equatorial  plate. 

With  the  formation  of  the  equatorial  plate  and  central  spindle, 
the  prophase  ends.  Variations,  too  numerous  to  describe,  occur, 
but  the  above  is  the  usual  course  in  this  stage  of  mitosis. 

Metaphase. — This  is  the  stage  during  which  the  chromosomes 
divide  and  separate.  Itjroncerns  the  chromatin  chiefly  and  is  of 
short  duration. 


Fig.  32. — Scheme  of  the  Daughter 
Stars.     (Stohr's  Histology.) 


Fig.  33. — Scheme  of  Division  of  the 
Protoplasm  forming  Daughter 
Cells.     (Stohr's  Histology.) 


The  chromosomes  divide  longitudinally  into  two  equal  portions. 
This  cleavage  occurs  at  the  closed  end  first,  and  as  it  proceeds,  the 
daughter  chromosomes  become  separated,  one-half  being  drawn  to- 
ward the  one  centrosome,  and  the  other  toward  the  second.  This 
gives  rise  to  a  second  spindle,  the  nuclear,  or  chromatic  spindle. 
The  separation  is  affected  by  the  traction  exerted  upon  the  daughter 
chromosomes  by  the  threads  of  the  central  spindle. 

Anaphase. — This  is  the  stage  of  complete  separation  of  the  chro- 
mosomes. The  latter  collect  around  their  respective  centrosomes, 
and  remain  connected  to  the  opposite  set,  for  some  time,  by  the 
central  spindle  threads.  The  figures  thus  formed  are  the  diasters, 
or  daughter  stars. 

Telophase. — This  stage  is  concerned  with  the  cytoplasmic 
changes  and  the  formation  of  a  resting  nucleus.  Up  to  this  time, 
the  cytoplasm  has  been  practically  quiescent. 


THE    OVUM  71 

The  chromosomes  collect  around  the  centrosomes,  and  unite  to 
form  a  close  skein.  Lateral  twigs  are  developed  that  anastomose 
to  form  the  nuclear  network,  a  nuclear  membrane  is  formed  and 
a  nucleolus  appears. 

The  hitherto  inert  cytoplasm  shows  changes.  A  plate  of  granules 
{cell-plate)  appears  at  the  equator  of  the  cell,  and  separation  occurs 
in  the  intervening  space  until  two  separate  masses  are  formed; 
these  are  the  daughter  cells.  Frequently  the  centrosome  divides 
at  this  stage  forming  a  diplosome. 

The  above  changes  are  usually  succeeded  by  a  period  of  rest. 

Although  apparently  a  long  process,  only  about  one-half  hour  is 
consumed  in  the  division  of  human  cells,  but  the  cells  of  lower 
animals  require  a  longer  period  (three  hours). 

In  the  case  of  giant  cells,  the  nucleus  divides  and  redivides,  while 
the  cytoplasm  remains  unchanged.  They  may  also  be  formed  by 
the  fusion  of  the  cytoplasm  of  a  number  of  cells  with  the  reten- 
tion of  the  individuality  of  the  nuclei. 

As  all  cells  are  developed  from  preexisting  elements,  it  is  but 
natural  that  the  original  cell  of  the  body,  the  ovum,  should  be  of 
greatest  interest.  It  is  the  most  characteristic  cell  of  the  body, 
and  is  secreted  by  the  ovary.  It  is  the  largest  cell,  and  illustrates 
the  individual  parts  well. 

The  ovum  consists  of  a  limiting  wall,  the  vitelline  membrane, 
that  may  be  well  developed.  Within  this  is  the  cytoplasm,  vitellus, 
which  consists  of  two  parts — the  deutoplasm,  or  nutritive  yolk,  and 
the  animal  protoplasm,  or  formative  yolk.  This  is  of  importance, 
embryologically.  Within  the  vitellus  is  found  the  nucleus,  or  ger- 
minal vesicle,  which  contains  a  deeply  stained  nucleolus,  or  germinal 
spot.  The  centrosome  is  to  be  seen  in  unripened  ova.  After  matu- 
ration this  body  disappears.  In  what  might  be  termed  an  embryologic 
ovum,  there  are  two  layers  external  to  the  vitelline  membrane,  the 
zona  pellucida  and  the  corona  radiata.  Of  these,  the  former  is 
the  more  important,  because  of  the  'part  which  it  plays  in  the  early 
stages  of  development. 

There  are  a  number  of  processes  that  occur  in  the  ovum  before 
it  can  develop  into  an  offspring.  Of  these,  the  most  important  are 
MATURATION  and  FERTILIZATION.     The  former  occurs,  usu- 


~2  PRACTICAL   HISTOLOGY 

ally,  in  the  ovary,  or  shortly  after  ovulation,,  and  the  latter,  as  a 
rule,  in  the  oviduct. 

Maturation  is  the  process  by  which  part  of  the  chromatin  and  a 
small  portion  of  the  cytoplasm  are  extruded  in  the  form  of  two 
minute  structures  called  polar  bodies.  It  is  a  modified  karyokinesis, 
and  its  object  is  unknown.  All  ova  must  pass  through  this  process 
before  they  can  be  fertilized. 

Fertilization  is  the  process  in  which  the  male  and  female  elements 
unite  to  form  a  complete  and  perfect  cell,  which,  by  division,  gives 
rise  to  the  cells  that  ultimatelv  form  the  whole  bodv. 


Fig.  34. — Unripened  Ovum  from  a  Young  Guinea-pig. 
A.  Nucleus;  B,  nucleolus;  C,  centrosomes  in  the  attraction  sphere. 

The  male  element,  or  spermatozoon,  or  spermium,  consists  of 
head,  middle-piece  and  tail.  Of  these  the  head  and  middle-piece 
representing  the  nucleus  and  centrosome,  respectively,  of  a  cell  of 
the  testicle,  enter  the  ovum  and  form  eleven  or  twelve  chromosomes. 
The  chromatin  of  the  germinal  vesicle  of  the  ovum  also  forms 
twelve.  Bv  longitudinal  cleavage  forty-sis  or  forty-eight  are  formed 
of  which  iwenix-three  or  twenty-four  enter  into  each  diaster  and, 
consequently,  each  daughter  cell.  By  this  process  the  descendants 
of  the  fertilized  ovum  contain  double  the  number  of  chromosomes  that 
existed  in  either  of  the  original  cells  before  fertilization.  Through  the 
male  and  female  chromatin  the  offspring  receives  the  characteristics 
of  its  parents. 


THE    TRIPLOHLAM  7- 

One-half  of  the  spermia  contain  eleven  chromosomes  and  the 
other  half  contain  twelve.  The  ovum  always  contains  twelve.  If 
the  ovum  is  fertilized  by  a  spermium  containing  twelve  chromosomes 
the  offspring  will  be  a.  female.  If  the  fertilizing  spermium  contained 
only  eleven  chromosomes  the  offspring  will  be  a  male.  The  male 
somatic  cells  are  said  to  contain  but  twenty-three  chromosomes 
while  the  somatic  cells  of  the  female  contain  twenty-four 
chromosomes. 

After  fertilization  the  ovum  divides  and  redivides,  forming  an 
irregular  mass  of  cells  called  the  morula,  or  mulberry  mass.  Certain 
of  these  cells  form  a  complete  layer  that  surrounds  the  remainder, 
which  constitutes  an  irregular  mass.  The  layer  is  the  outer  cell- 
mass  and  the  latter  the  inner  cell-mass.  This  structure  con- 
stitutes the  blastula,  or  one-layered  vesicle.  Of  these  two  structures 
the  inner  is  the  more  important  as  it  persists  and  forms  the  whole 
body  /while  the  outer  assists  in  the  imbedding  of  the  ovum  and  the 
formation  of  the  placenta. 

The  inner  cell-mass  forms  two  layers,  an  outer,  several  cells 
in  thickness,  the  ectoderm,  or  epiblast,  and  an  inner,  composed 
of  but  a  single  layer,  the  entoderm,  or  hypoblast.  This  is  the 
gastrula,  or  diploblast.  The  ectoderm  and  entoderm  each  set 
aside  a  number  of  cells  which  by  multiplication  form  a  third  layer, 
the  mesoderm,  or  mesoblast,  that  lies  between  the  two.  This 
structure  receives  the  name  of  blastodermic  vesicle,  or  triploblast. 

From  these  three  primitive  layers  all  the  organs  and  tissues  of 
the  body  are  formed  as  follows: 

Ectoderm. 

The  nerve  system  (cerebrospinal  and  sympathetic)  the  retina, 
the  bulk  of  the  crystalline  lens,  the  muscle  of  the  iris  and  part  of 
the  vitreous  humor  of  the  eyeball,  the  epithelium  of  the  cornea 
and  conjunctiva,  the  epithelium  of  the  internal  ear  and  of  the  olfac- 
tory organ,  the  medulla  of  the  adrenal. 

The  epithelial  lining  of  the  penile  portion  of  the  male  urethra, 
the  labia  of  the  female  and  the  glands  leading  thereto. 

The  epithelial  lining  of  the  mouth  and  salivary  glands,  epithelial 
lobe  of  the  pituitary  body,  the  enamel  of  the  teeth,  the  cells  of  the 
nasal  tract  and  glands  leading  thereto,  to  the  pharynx,  and  the  lining 
of  the  anus. 


74  PRACTICAL  HISTOLOGY 

The  epidermis  and  appendages  of  the  skin,  muscles  of  the  sweat 
glands. 

The  syncytium  of  the  placenta. 
The  notochord  {primarily). 

Entoderm. 

The  epithelial  lining  of  the  bladder,  the  prostate  and  glands  of 
Cowper,  of  the  prostatic  and  membranous  portions  of  the  male  and 
entire  female  urethra,  vestibule  and  glands  of  Bartholin. 

The  epithelium  of  the  tongue,  thymus  and  thyroid  bodies  of  the 
parathyroids,  middle  ear  and  Eustachian  (auditory)  tube. 

The  epithelium  of  the  alimentary  and  respiratory  tracts  from  the 
mouth  and  posterior  nares  down  and  the  epithelium  of  all  glands 
opening  into  these  structures. 

The  notochord  {secondarily). 

Mesoderm. 

The  vascular  system. 

The  lymphatic  system  including  the  large  serous  cavities,  spleen 
and  thymus  body  (except  the  corpuscles  of  Hassal). 

The  muscle  tissues  (except  the  muscles  of  the  sweat  glands  and 
iris) . 

The  connective  tissues. 

Testicles,  vas,  seminal  vesicles,  ejaculatory  ducts,  ovaries,  oviducts, 
uterus  and  vagina. 

Kidneys,  ureters  and  cortex  of  adrenals.    . 


CHAPTER  III 
THE  TISSUES 

From  the  preceding  table  it  will  be  seen  that  all  tissues  are  de- 
veloped from  the  three  layers  of  the  triploblast.  These  tissues  are 
grouped,  histologically,  under  four  classes,  epithelial,  connective, 
muscle  and  nerve. 

A  tissue  consists  of  similarly  differentiated  cells  held  together  by 
intercellular  substance  and  performing  a  definite  function.  The 
intercellular  substance  varies  with  the  different  tissues.  The  cells 
of  a  tissue  may  be  so  arranged  as  to  form  an  organ  or  merely  a 
supporting  structure. 

A  syncytium  is  a  tissue  in  which  the  cell  boundaries  have  never 
appeared  or  have  disappeared.  It  arises  through  the  continued 
division  of  the  nucleus  without  the  attendant  division  of  the  proto- 
plasm, or  through  the  fusion  of  a  great  number  of  cells  with  an  attend- 
ant* loss  of  cell  boundaries.  It  represents  an  extensive  mass  of 
nucleated  protoplasm. 

EPITHELIUM 

The  epithelial  tissues  are  characterized  by  the  small  amount  of  the 
intercellular  cement.  The  cellular  elements  are  usually  promi- 
nent, and  rich  in  granular  cytoplasm.  They  are  found  lining 
cavities  and  covering  surfaces  that  communicate  normally  with  the 
air  and  usually  secrete,  although  they  may  also  have  an  excretory, 
absorptive,  or  protective  function  or  receive  sense  impressions 
(special  sense).  Lymph  spaces  may  exist  between  them  and  nerve 
fibers  terminate  upon  them.  They  are  soft  and  vary  considerably 
in  shape  in  the  different  organs.  As  the  shape  is  constant  for  the 
various  varieties  this  condition  lends  itself  to  the  classification  of 
epithelium.  In  some  hollow  organs,  however,  the  form  of  the  cells 
varies  considerably  at  different  times  depending  upon  the  degree 

75 


7r>  PRACTICAL   HISTOLOGY 

of  distension  (urinary  bladder  i.  Epithelial  tissues  are  avascular 
and  may  be  derived  from  any  of  the  layers  of  the  triploblast.  The 
cells  vary  in  size,  form  and  arrangement,  as  will  be  seen  later. 
Simple  epithelial  cells  either  secrete  or  assists  in  secretion  while  the 
stratified  cells  usually  have  a  protective  function. 

The  epithelial  cells  may  be  arranged  in  a  single  layer  of  elements 
and  this  constitute  is  called  simple  epithelium.  When  several  layers 
oi  cells  are  present  the  form  is  then  stratified  epithelium.  In  the  latter 
case  the  variety  takes  its  name  from  the  surface  cells  as  will  be  seen 
later.  In  this  form  the  basal  cells  are  always  columnar  elements 
and  the  intermediate  cells  are  polyhedral.  The  superficial  cells 
of  a  stratified  epithelium  are  derived,  by  division,  from  the  lower 
layers  and  when  these  superficial  elements  are  cast  off  they  are 
replaced  by  cells  from  the  layer  beneath  them.  In  the  simple  epithe- 
lia  when  a  few  cells  are  lost  they  are  readily  replaced  by  the  re- 
production of  the  neighboring  cells  but  when  a  large  surface  or  area 
is  destroyed  or  lost  then  the  replacement  is  very  difficult  or  impos- 
sible. In  the  latter  instance  the  condition  leads  to  serious  patho- 
logic conditions. 

The  intercellular  substance,  or  cement  varies  in  quantity.  Between 
the  columnar  cells  of  the  stomach  and  intestine  it  is  usually  abundant, 
especially  so  near  the  distal  extremities  of  the  cells  where  it  forms 
what  is  known  as  the  urminal  bars,  this  intercellular  cement 
responds  readily  to  silver  nitrate  staining  method. 

For  convenience  of  description,  the  cells  are  classified  as  follows: 

i.  Squamous.  2.  Columnar. 

(a)  Simple.  (c)  Simple. 

(b)  Stratified,  (d)  Stratified. 
Modified.  5.  Transitional  cells. 

3.  Ciliated.  6.  Pigmented. 
(e)  Simple.  Specialized. 

(/)  Stratified.  7.  Neuroepithelial. 

4.  Goblet  cells.  S.  Glandular. 

1.  Squamous. —  a  The  simple  squamous  cells  consist  of  a 
single  layer  of  flattened  elements,  each  containing  a  large  nucleus. 


EPITHELIUM 


77 


This  is  usually  in  the  center,  and  has  an  oval,  or  round  form.  The 
cytoplasm  may  constitute  so  thin  a  layer  that  the  nucleus  produces 
a  bulge.  They  occur  in  the  descending  limb  of  Henle's  loop,  the 
capsule  of  Bowman  in  the  kidney,  the  alveoli  of  the  lungs,  and  in 
parts  of  the  ventricles  of  the  brain. 

(b)  The  stratified  squamous  variety  consists  of  many  layers  of 
cells  that  are  unlike  in  form.     The  lowest  layer,  the  germinal  stratum, 


a. 


Fig.  35. 
(a)   Simple  squamous  cells,     (b)   Simple  cuboidal  cells. 


Fig.  37. — Squamous 
Cell  Isolated. 


Fig.  36. — Surface  View  of  Squamous      Fig.  38. — Stratified  Squa- 
Cells  of  Frog's  Skin.  mous  Epithelium. 


is  columnar,  while  those  cells  just  above  are  polygonal.  The 
succeeding  cells  become  more  and  more  flattened,  forming  the 
squames,  or  scales,  from  which  this  variety  receives  its  name.  These 
scales  may  overlap  one  another  and  be  keratinized,  as  in  the  skin. 
The  cells  of  the  deeper  layers  of  all  stratified  epithelium  are  all  sepa- 
rated from  one  another  by  spaces  bridged  by  protoplasmic  processes 
that  connect  the  various  cells  together.     These  spaces  vary  in  extent 


7S 


PRACTICAL  HISTOLOGY 


at   different   times.     These   elements   were   formerly   classified   as 
prickle  cells. 

In  stratified  epithelium  the  number  of  layers  varies  from  five  to 
thirty  or  more.     The  stratified  squamous  variety  has  the  greatest 


Fig.  39. — Skin-  of  the  Palm  of  a  Child  at  Birth  Showing  Stratified 
Squamous  Epithelium.  (Radasch,  Reference  Handbook  of  the  Medical 
Sciences.) 

number.  The  cells  of  the  deeper  layers  are  all  soft  and  show  karyo- 
kinetic  figures,  indicating  reproduction  that  gives  the  cells  of  the 
superficial  layers.  Toward  the  surface  the  cells  become  harder  and 
ultimately  keratinized  forming  then  the  protective  scales  of  the 
surface  of  the  layer.     The  amount  of  keratinization  depends  upon 


EPITHELIUM 


79 


the  location  of  the  layer;  upon  the  surface  of  the  body  where  the  great- 
est amount  of  protection  is  desired  the  keratinization  is  most  extensive. 
Even  here  it  varies  according  to  the  use  of  the  part;  upon  the  soles 
and  palms,  where  the  skin  is  most  used,  the  layer  of  keratinized 
scales  is  thickest;  upon  the  outer  parts  of  the  upper  and  lower 
extremities  and  the  back  (most  exposed  parts)  it  is  next  in  quantity; 
upon  the  inner  parts  of  the  extremities  and  the  ventral  thoracic 
wall  it  is  less  marked.  The  dryness  of  all  of  these  parts,  due  to  the 
constant  and  rapid  evaporation  of  the  perspiration,  is  an  important 
factor  in  this  process  of  keratinization.     In  those  parts  of  the  body 


Fig.  40. — Stratified  Squamous  Cells  Showing  Prickle  Cells. 
(Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 


supplied  with  stratified  squamous  epithelium,  but  where  there  is 
constant  moisture  (mouth,  esophagus,  lips,  vagina,  etc.),  the  amount 
of  keratinization  is  at  a  minimum  in  man.  In  lower  animals  the 
keratinization  of  the  epithelium  of  the  tongue  and  esophagus  is  more 
marked  than  upon  the  surface  of  the  body. 

This  process  of  keratinization  is  a  chemical  change  and  is  accom- 
panied by  changes  in  the  nucleus.  The  process  starts  in  the  cells 
above  the  prickle  layer.  The  nucleus  becomes  less  chromatic  and 
somewhat  flattened  and  the  cells  body  likewise  becomes  elongated. 
The  cytoplasm  shows  a  number  of  coarse  granules  of  eleidin  and 
keratohyalin  and  as  the  process  continues  the  cells  become  more 
scale-like  and  keratin  is  formed.  By  this  time  the  cells  in  which 
these  changes  have  been  produced  are  near,  or  at  the  surface,  to 


8o 


PRACTICAL    HISTOLOGY 


which  region  they  have  been  pushed  by  the  reproduction  of  the  cells 
underneath  and  the  desquamation  of  the  cells  superficial  to  them. 

Stratified  squamous  cells  are  found  covering  the  body  as  the 
epidermis,  lining  the  mouth,  tongue,  pharynx,  esophagus,  epiglottis, 
vocal  cords  and  the  anus  and  vagina. 

2 .  Columnar. —  Y  Simple  columnar  cells  are  tall,  cylindric  elements 
arranged  in  a  single  layer.  The  nucleus  is  usually  oval,  and  found 
nearer  the  base  than  the  center  of  the  cell.     Protoplasmic  bridges 


_^._J.,  -  i  J  <   I   1    i    i!__L,.i-        ' 


&  to  ^ 

Fig.  41. 

a.     Simple     columnar     showing    cuticular    border,     b.     Simple    ciliated    cells. 

c.  Simple  columnar  and  goblet  cells. 


Fig.  42. 
a.    Isolated    columnar    cells.     6.    Isolated    ciliated    cells,     c.    Three   stages  of 

goblet  cells. 


are  said  to  exist  and  the  intercellular  cement  is  usually  abundant, 
forming  the  terminal  bars.  The  cytoplasm  may  be  granular  or 
fibrillar  and  contain  fat  or  other  products.  The  appearance  of  the 
cytoplasm  usually  depends  upon  the  state  of  secretory  activity 
of  the  cell. 

The  variety  is  found  in  the  stomach  and  intestinal  tract,  the 
penile  portion  of  the  urethra,  glands  of  Cowper  and  Bartholin, 
prostate,  gall-bladder  and  seminal  vesicles,  and  in  many  gland  ducts. 
In  the  intestine  these  cells,  upon  their  exposed  surface,  have  a  layer 


EPITHELIUM 


8l 


of   differentiated   cytoplasm  forming  a  partial  membrane;  this  is 
called  a  cuticular  border.    Low  columnars  are  often  called  cuboidal. 

Pseudo stratified  cells  are  simple  columnar,  or  ciliated,  cells,  in 
which  the  nuclei  are  not  all  basal,  but  occupy  different  levels,  thus 
giving  the  appearance  of  several  layers  of  cells,  where,  in  reality, 
but  a  single  layer  exists.      These  are  found  as 
ciliated   elements   in   the  oviducts,  uterus  and 
middle  ear  and  as  nonciliated  elements  in  the 
seminal  vesicles  (maybe  simple)  and  prostate, 
according  to  some  writers. 

(d)  Stratified    columnar    cells    consist    of   a 
number  of  layers  of  columnar  elements  super- 
imposed upon  one  another.     The  cells  are  not 
as  large  as  the  preceding.     They  occur  in  the  vas  deferens,  mem- 
branous urethra  and  the  ducts  of  some  glands. 

3.  Ciliated  Cells. — (e)  Simple  ciliated  cells  are  simple  columnar 
elements,  which  bear,  upon  their  exposed  surface,  a  varying  number 
of  hair-like  processes  called  cilia.  These  possess  a  motion  that  is 
directed  toward  the  outlet  of  the  organ  in  which  these  cells  are 


Fig.  43. — Pseudo- 
stratified  cells. 


Fig.  44. 
a    Stratified  columnar  cells,     b.  Stratified  ciliated  cells,     c.  Stratified  columnar 

cells  showing  goblet  cells. 


found.  It  is  said  that  in  lower  animals  the  action  of  the  cilia  can  be 
reversed.  They  line  the  smaller  bronchioles,  spinal  canal,  accessory 
spaces  of  the  nasal  fossae  and  the  ventricles  of  the  brain. 

Within  the  cell  each  cilium  is  connected  with  a  pair  of  granules 
called  basal  body;  these  latter  are  centrosomic  in  origin.  As  these 
basal  bodies  are  not  present  in  the  cells  of  the  epididymis  and  spinal 


82 


PRACTICAL  HISTOLOGY 


canal  their  cilia  are  not  considered  true  cilia.     The  cytoplasm  may 
contain  vacuoles,  pigment  granules  and  even  secretory  granules. 
(f)  The  stratified  ciliated  cells  are  practically  stratified  columnar 


-■ 


-3£> 


Fig.  45. — Ciliated  Cells  Showing  the  Basal  Particles.     The  middle  cell 
shows  a  diplosome.      (After  von  Lenhossek.) 


■A    \&  1 


Fig.  46. 
a,  Stratified  columnar  cells  of  the  vas  deferens  of  a  guinea-pig  showing  a  cuticular 
border,     b,  Stratified  ciliated  cells  of  the  trachea  of  a  child  at  birth  showing 
a  cuticular  border.      (Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 

cells,  of  which  the  exposed  layer  alone  possesses  cilia.  They  are 
found  in  the  epididymis,  first  part  of  the  vas,  Eustachian  tube, 
upper  part  of  the  pharynx,  in  the  larynx,  trachea  and  nasal  tract. 


EPITHELIUM  &3 

4.  Goblet  cells  are  cells  of  the  cylindric  type,  distended  with  a 
peculiar  secretion  called  mucin.  They  really  represent  unicellular 
glands.  When  these  cells  are  filled  they  resemble  goblets,  hence  the 
name.  The  secretion  makes  its  appearance  in  the  form  of  granules 
(mucinogen)  which  increase  in  number  and  size  and  respond  to 
special  stains  (muchematein).  When  secretion  occurs  the  granules 
absorb  water,  swell  and  coalesce  to  form  a  single  droplet.  When  the 
secretion  has  been  discharged  the  cells  are  long  and  slender,  the 
part  containing  the  nucleus  projecting  on  either  side.  These  cells 
are  met  with  in  the  gastro-intestinal  and  respiratory  tracts. 

5.  Transitional  cells  represent  a  peculiar  intermediate  form  of 
protective  epithelium  between  the  stratified  squamous  and  stra  tified 
columnar  varieties.  The  genetic  layer  con- 
sists of  columnar  cells  and  these  are  succeeded 
by  several  layers  of  polygonal  or  pyriform 
elements.  The  surface  cells  vary  as  follows: 
in  the  bladder  and  ureter,  when  empty,  these 
cells  are  polygonal  or  cuboidal,  while  in  the 

distended  bladder   they   are   flattened.      In 

.  ,  ,  .  ,    ,    j     ,        ,_,.       Fig.  47. — Transitional 

the  urethra  they  remain  polyhedral.      Inis  Cells. 

variability   of   shape  indicates   the  elasticity 

and'  extensibility  of  epithelium,  as  pointed  out  by  Harvey. 

Keratinization  of  this  variety  seldom  occurs  and  the  shape  of  the 
cells  is  so  characteristic  that  they  can  readily  be  distinguished  from 
vaginal,  urethral  and  epidermal  cells  in  the  urine. 

This  variety  is  found  in  the  pelvis  of  the  ureter,  the  ureter,  bladder, 
first  portion  of  the  male  urethra  and  the  greater  portion  of  the  female 
urethra. 

6.  Pigmented  cells  are  polygonal,  or  columnar  elements  in  which 
the  cytoplasm  contains  a  number  of  pigment  granules.  This  pig- 
ment may  be  diffuse  or  granular  in  character  and  is  probably  intra- 
cellular in  origin.  The  polygonal  cells  are  found  in  the  epidermis 
of  colored  races  and  around  the  nipples  and  genitals  of  Caucasians. 
In  the  retina  of  the  eyeball  the  cells  are  irregular  in  form  and  the 
position  of  the  pigment  depends  upon  whether  the  retina  has  been 
fixed  with  the  exclusion  of  light  or  not.  The  pigment  granules  may 
be  so  numerous  as  to  obscure  the  various  parts  of  the  cell. 


84 


PRACTICAL   HISTOLOGY 


7.  Neuro-epithelial  cells  are  epithelial  cells  that  have  become  so 
differentiated  as  to  perform  a  special  sense  function.  They  differ 
according  to  location,  and  will  be  described  under  each  special  sense. 
They  occur  in  the  retina  (rods  and  cones),  in  the  internal  ear  (hair 
cells),  in  the  olfactory  mucous  membrane,  (olfactory  cells)  in  the  taste- 
buds  (gustatory  cells)  and  as  tactile  cells. 


Fig.  48. — Pigmented  Cells  of  the  Human  Retina  (Surface  View). 

a.  Cell  showing  pigmented  processes.     (After  Greef  from  the  Reference  Handbook 

of  the  Medical  Sciences.) 

8.  Glandular  cells  are  concerned  with  secretion  or  excretion  and 
vary  according  to  the  nature  of  the  gland  in  which  they  are  found, 
as  in  the  liver,  pancreas,  etc.  The  cytoplasm  is  usually  granular 
indicating  the  formation  of  a  secretion.  Immediately  after  secre- 
tion the  cytoplasm  is  usually  clear. 


MUCOUS  MEMBRANES 

Mucous  Membranes. — Within  the  body  proper  are  a  number  of 
recesses  and  tracts  that  communicate  normally  with  the  exterior; 


EPITHELIUM 


85 


these  are  lined  with  epithelial  cells  that  are  supported  in  an  especial 
manner,  constituting,  thus,  mucous  membranes.  These  in  themselves 
are  quite  extensive,  but  their  area  is  greatly  increased  by  offshoots 
in  the  form  of  glands,  ducts,  recesses,  folds  and  projections  (villi). 
These  tracts  are  the  alimentary,  respiratory,  urinogenital  systems 
and  lacrimal  apparatus  and  their  connected  glands  and  cavities. 


Fig.  49. — Glandular  Epithelial  Cells. 
A,  Tubules  of  the  human  thyreoid  gland  showing  cuboidal  cells.     B,  Tubules  of 
a  human  submaxillary  gland;  a,  tubule  showing  a  demilune;  b,  cross-section 
of  a  tubule.     (Radasch,  Reference  Handbook  of  the  Medical  Science.) 

To  any  and  all  of  these  the  air  has  access.  They  all  have  their 
beginnings  or  endings,  or  both,  at  the  skin  and  the  line  of  connection 
is  usually  sharply  marked.  The  lining  of  each  tract  may  differ 
somewhat  from  that  of  another,  as  their  functions  are  not  the  same 
but  the  general  structure  is  the  same  in  all  cases. 

These  membranes  are  firmly  attached  to  the  underlying  structures 
in  certain  regions,  as  in  the  nasal  cavities  and  their  accessory  fossae; 
in  other  regions,  as  the  stomach,  bladder,  etc.,  the  connection  is 
rather  loose  permitting  of  considerable  distention  of  these  organs 
without  injury  to  the  lining  membrane.     In  some  organs  the  mucous 


86  PRACTICAL  HISTOLOGY 

membrane  is  nearly  even  and  regular  in  course,  as  gland  ducts; 
in  others  it  is  formed  into  finger-like  projections  (villi),  as  in  the 
small  intestine.  In  still  other  organs  it  is  thrown  into  extensive 
folds,  as  the  intestines,  stomach  and  bladder.  By  the  formation 
of  villi  and  folds  the  absorptive  and  secretory  surfaces  are  enormously 
increased  without  a  marked  increase  of  the  bulk  of  the  organ. 

Normally  mucous  membranes  are  soft,  opaque,  or  nearly  so, 
slimy  and  easily  torn  by  moderate  force.  Ordinarily  they  are 
pinkish  in  color  but  the  depth  of  color  depends  on  the  organ  and 
its  function.  The  color  is  due  to  the  vascularity  of  the  part  and  natu- 
rally where  the  vascularity  is  greater,  the  color  will  be  deeper,  as  for 
instance,  in  the  stomach,  pharynx  and  rectum.  The  color  is  deeper 
in  the  fetus  and  infant  than  in  the  adult. 

A  typic  mucous  membrane  consists  of  four  layers,  (i)  epithelium, 
(2)  basement  membrane  (3)  tunica  propria,  (4)  muscularis  mucosa. 

1.  The  epithelium  may  be  of  any  variety  and  will  depend  upon  the 
function  of  the  membrane.  In  such  regions  where  protection  alone 
is  desired  the  epithelium  is  stratified  squamous,  transitional,  or 
stratified  columnar.  Where  secretion  and  excretion  are  being  carried 
on.  the  variety  is  simple  columnar,  cuboidal  or  goblet.  Where 
protection  is  desired  and  where,  at  the  same  time,  the  removal  of 
small  foreign  bodies,  entangled  in  mucus,  must  be  maintained,  the 
variety  is  either  simple  or  stratified  ciliated. 

2.  The  basement  membrane  is  not  always  demonstrable  and  when 
noticeable  it  is  thin  and  apparently  homogeneous.  It  usually 
consists  of  flattened  cells  that  form  a  continuous  layer  or  may  be 
united  to  one  another  by  protoplasmic  processes,  making  thus,  a 
sort  of  network.  Some  state  that  it  is  secreted  by  the  epithelial 
cells  but  in  all  probability  it  is  derived  from  the  tunica  propria. 

3.  The  tunica  propria  consists  of  a  delicate  network  of  fibroelastic 
tissue  that  varies  in  different  organs.  In  some  organs  (esophagus) 
the  white  fibrous  tissue  predominates  and  is  more  closely  packed 
and  therefore  tougher.  In  other  organs,  as  stomach  and  intestines, 
it  is  looser  as  glands  and  lymphoid  tissue  in  great  abundance  are 
found  here.  It  is  this  layer  that  supports  the  capillary  blood-vessels, 
smaller  lymph  channels  and  the  smaller  nerve  trunks  and  fibers. 
Here  are  also  found,  in  certain  organs,  glands  and  lymphoid  tissue. 


MUCOUS    MEMBRANES  .      87 

In  the  small  intestine  the  tunica  propria  is  thrown  into  an  enormous 
number  of  finger-like  projections  called  villi.  These  structures  are 
of  the  greatest  importance  in  the  absorption  of  the  digested  food 
products. 

4.  The  muscularis  mucosa  is  not  present  in  all  mucous  membranes. 
It  consists  of  involuntary  nonstriated  muscle  tissue  arranged  in  two 
layers.  The  fibers  of  the  inner  layer  run  transversely  while  those 
of  the  outer  layer  run  longitudinally. 

The  functions  may  be  classed  as  absorption,  secretion,  excretion 
and  protection. 

1.  Absorption. — As  a  result  of  the  action  of  digestive  fluids  the 
food  ingested  is  converted  into  substances  that  are  absorbable.  This 
process  is  carried  on  chiefly  by  the  villi  of  the  small  intestine.  By 
a  "selective  action"  of  the  simple  columnar  epithelial  cells  covering 
the  villi  the  water  and  inorganic  salts  are  passed  through  and  ulti- 
mately reach  the  blood-vessels.  All  of  the  sugars,  except  possibly 
lactose,  are  converted  into  levulose  or  dextrose  and  as  such  are 
taken  into  the  epithelial  cells  and  transferred  to  the  blood-vessels. 
In  whatever  form  the  carbohydrates  are  absorbed  they  never 
leave  these  cells  except  in  the  form  of  levulose  or  dextrose.  Proteins 
are  converted  into  peptones  by  the  digestive  fluids  and  as  such  are 
absorbed  by  the  epithelial  cells  of  the  villi.  Native  proteins  are 
also  absorbed  by  the  mucosa  of  the  large  intestine.  After  absorption 
the  epithelial  cells  convert  these  peptones  into  plasma-albumen  and 
as  such  are  given  over  to  the  blood-vessels.  Recent  investigation 
seems  to  point  to  the  fact  that  the  end  products  of  protein  digestion 
are  not  peptones  but  less  complex  bodies,  as  polypeptids,  peptids 
and  amido-acids.  It  is  these  simpler  products  that  these  epithelial 
cells  convert  into  plasma-albumen  and  plasma-globulin.  Fats  are 
believed,  by  some  investigators,  to  be  converted  into  an  emulsion 
during  digestion  and  from  this  emulsion  the  fat  globules  are  taken 
by  the  epithelial  cells  and  passed  through  them  to  the  lymph  vessels. 
Others  believe  that  as  a  result  of  digestion,  fats  are  converted  into 
soaps  and  glycerin.  The  epithelial  cells  take  these  and  reconstruct 
fats  within  the  cell-body  and  the  fat  is  then  passed  to  the  lymph 
vessels  where  with  the  lymph  it  constitutes  chyle. 

2.  Secretion. — This  term  is  applied  to  the  fluid  that  is  made  by 


88  PRACTICAL   HISTOLOGY 

the  vital  activities  of  the  epithelial  cells  from  the  constituents  of 
the  lymph  that  surrounds  them.  This  juice  is  used  in  the  vital 
processes  of  the  body.  Such  juices  are  the  pancreatic  and  gastric, 
saliva,  bile,  etc.,  and  the  various  internal  secretions.  These  fluids 
are  formed  as  the  results  of  chemical  changes  within  the  cells. 
That  the  epithelial  cells  of  the  stomach  give  rise  to  an  entirely  differ- 
ent juice  than  those  of  the  liver  or  other  glands  is  probably  due  to 
the  difference  in  histologic  and  chemical  structure.  These  epithelial 
elements  are  not  always  active  but  discharge  their  secretions  at 
periodic  intervals  and  in  between  enjoy  a  period  of  rest  and  re- 
cuperation. During  the  inactive  period  certain  substances,  as  mucin, 
glycerin,  proteins  and  antecedents  of  enzymes,  accumulate  in  the 
cells,  as  the  result  of  cellular  activity;  these  substances  constitute 
the  secretion.  At  such  times  the  blood  supply  is  not  great.  During 
glandular  activity  the  organ  becomes  red,  due  to  increased  vas- 
cularity, and  as  a  result  a  rapid  transudation  of  water  and  salts 
into  the  lymph  spaces  occurs.  As  the  water  passes  through  the 
cells  the  above-mentioned  constituents  are  dissolved  and  are  ulti- 
mately discharged  into  the  lumen  of  the  ducts. 

The  formation  and  discharge  of  the  secretions  are  controlled  by 
the  nerve  system.  These  nerve  centers  may  be  excited  by  emotional 
states  or  by  impressions  upon  the  terminals,  as  for  instance,  the 
flow  of  saliva  is  increased  either  by  the  presence  of  desirable  food 
in  the  mouth,  or  by  the  mere  thought  or  odor  of  desirable  food. 

3.  Excretions. — The  formation  and  elimination  of  waste  products 
which,  if  retained,  would  lead  to  injurious  results,  constitute  excre- 
tion. These  waste  products  are  emptied  into  the  blood  and  are  the 
results  of  the  activities  of  the  cells  and  tissues.  Epithelial  cells  are 
the  prime  factors  in  excretion  and  are  assisted  by  osmosis  and 
filtration.  The  chief  excretions  are  the  urine,  perspiration  and  bile. 
The  urea  and  salts  of  the  urine  are  not  made  by  the  kidneys  but  are 
merely  eliminated  by  these  organs.  The  epithelial  cells  of  the  kidney 
have  a  selective  power  by  means  of  which  they  take  these  substances 
from  the  blood  and  simply  pass  them  into  the  uriniferous  tubules. 
The  liver  does  not  make  the  cholesterin  (the  excrementitious  part 
of  the  bile)  but  merely  removes  it  from  the  blood  and  passes  it  to 
the  intestine.     The  sweat  glands  merely  remove  a  small  amount 


SEROUS    MEMBRANES  89 

of  urea  and  certain  inorganic  salts,  by  selective  action,  and  these 
with  water  from  the  blood  constitute  perspiration. 

4.  Protection. — In  certain  organs  that  do  not  secrete  nor  excrete, 
a  protective  lining  alone  is  required,  as  in  the  mouth,  esophagus, 
bladder,  ducts  of  glands,  etc.  The  epithelial  cells  here  are  usually 
of  the  stratified  squamous,  stratified  columnar  or  transitional 
varieties. 

SEROUS  MEMBRANES 

Some  writers  classify  endothelial  cells  as  epithelial,  but  as  they 
are  not  they  will  be  considered  here  so  as  to  emphasize  the  differences 
between  them.  When  an  area  of  epithelial  cells  is  denuded  thereof 
this  area  is  covered,  or  healed,  by  the  extension  of  the  epithelial 
cells  at  the  edges.  If  this  denuded  area  is  not  too  large  the  entire 
part  is  soon  covered  by  these  extended  cells.  If  the  area  is  large 
then  small  islands  of  epithelium  taken  from  other  parts  of  the  body 
and  placed  upon  the  denuded  area  will  usually  grow  and  spread, 
thus  covering  the  uncovered  area.  On  the  other  hand  when  the 
endothelial  cells  of  a  serous  membrane  have  been  denuded  they  are 
replaced  by  cells  from  the  underlying  subendothelial  tissue  and  hence 
are  of  connective  tissue  origin.  The  structure  and  functions  of 
serous  and  mucous  membranes  differ;  lastly  the  course  of  inflam- 
mations of  these  two  membranes  is  so  different  that  the  lining  cells 
must  essentially  be  different.  Although  serous  membranes  are 
here  described  it  must  be  remembered  that  it  is  for  the  sake  of  com- 
parison and  not  because  endothelial  cells  are  considered  epithelial 
cells. 

Endothelial,  or  better  mesothelial,  cells  are  thin,  flattened  ele- 
ments possessing  a  projecting  nucleus.  This  is  because  the  layer  of 
cytoplasm  is  so  thin  that  the  diameter  of  the  nucleus  exceeds  it. 
They  are  very  irregular  in  outline,  having  serrated  edges,  plate- 
like in  the  serous  cavities  and  lanceolate  in  the  blood-vessels.  They 
are  held  together  by  a  small  amount  of  intercellular  cement  and  pro- 
toplasmic processes.  The  cytoplasm  is  usually  clear  and  apparently 
structureless  and  may  even  show  the  fibers  passing  from  cell  to  cell. 
The  free  surface  of  the  endothelial  cell  is  said  to  be  covered  by  a 
thin  layer  of  vertically  striated  cytoplasm.     At  intervals  the  cells 


go 


PRACTICAL   HISTOLOGY 


do  not  approximate  absolutely  forming  thus,  the  stigmata.  These 
are  supposed  to  be  openings  leading  into  lymph  spaces  and  vessels 
of  the  serous  cavities.  They  are  considered  by  some  as  mere  arti- 
facts. In  the  abdominal  peritoneum  of  the  frog  normal  openings, 
the  stomata,  exist;  these  are  bounded  by  specialized  guard  cells. 
The  endothelium  of  the  capillaries  is  said  to  be  contractile.     Endo- 


Fig.  50. 
A. — Abdominal  Endothelium,  a,  Endothelial  cell;  b,  nucleus  of  cell;  c, 
cell  boundary;  d,  stigmata;  e,  endothelial  cells  of  stomata;  /,  stomata. 
B. — Mesenteric  Endothelium.  C. — Arterial  Endothelium.  D. — 
Perivascular  Lymphatics,  a,  Endothelial  cells  of  lymphatics;  b,  blood- 
vessel (arteriole). 

thelial  cells  never  occur  in  more  than  a  single  layer  and  are  plate- 
like though  those  of  joint-cavities  may  have  a  cuboidal  form.  In 
this  they  resemble  the  fetal  mesothelial  cells  which  are  of  the 
cuboidal  type. 

A  serous  membrane  consists  of  two  parts:  (1)  a  single  layer  of 
endothelial  cells,  (2)  a  layer  of  sub  endothelial  tissue. 

1.  The  endothelial  cells  are  as  above  described.  These  rest 
directly  upon  the  fibroelastic  subendothelial  connective  tissue, 


GLANDS 


91 


2.  The  subendothelial  tissue  consists  of  a  thin  layer  of  areolar  tissue 
that  consists  of  a  delicate  network  of  white  fibrous  and  yellow  elastic 
tissues.  This  supports  the  blood-vessels  and  the  nerves.  Lymph 
spaces  are  very  numerous  and  if  stomata  really  exist  they  connect 
the  cavity  lined  with  these  lymph  spaces. 

Serous  membranes  are  quite  sensitive  being  well  supplied  with 
afferent  nerves.  In  the  peritoneum  these  terminate  in  bulb-like 
expansions;  around  joint  cavities  Pacinian  bodies  are  also  numerous. 

Serous  membranes  are  found  lining  joint-cavities,  bursae,  tendon 
sheaths,  the  circulatory  and  lymphatic  systems  and  the  larger 
serous  cavities,  the  pleural,  peritoneal  and  pericardial. 


Characteristics 

Mucous  membranes 

Serous  membranes 

Where  found 

Lining  cavities  that  com- 
municate normally  with 

In  cavities   that   do   not 

normally     communicate 

the  air. 

with  the  air  (female 
peritoneal  cavity  ex- 
cepted). 

Lined  by 

Epithelial    cells    of    any 
variety. 

Endothelial    (M  e  s  0- 

thelial)  cells,  one  layer. 

Secrete 

With     few     exceptions. 
Epithelial      cells,      base- 

Do not. 

Endothelial     cells,     sub- 

ment      membrane, 

endothelial      connective 

tunica        propria, 

tissue. 

muscularis         mucosae. 

Represents 

All     four     varieties     of 

But  two  varieties  (neither 

tissue. 

muscle  nor  epithelial 
tissues). 

Minot  considers  the  cells  that  line  the  pleural,  pericardial  and 
peritoneal  cavities  as  mesothelial,  while  those  of  the  circulatory  and 
lymphatic  systems  he  calls  endothelial. 


GLANDS 

A  description  of  epithelial  tissues  would  not  be  complete  without 
a  consideration  of  glands.  The  term  gland  is  loosely  applied  to 
some  organs  that,  strictly  speaking,  are  not  true  glands  in  the  sense 
of  epithelial  structure.     Most  of  the  glands  are  offshoots  or  deriva- 


92  PRACTICAL   HISTOLOGY 

tives  of  mucous  membranes  and  the  great  majority  still  retain  their 
connection  in  the  completed  condition.  Glands  may  be  unicellular, 
as  the  goblet-cell,  or  multicellular,  as  those  that  will  be  considered 
below.  A  gland  is  an  evagination  of  a  mucous  surface,  consists  of 
epithelial  cells,  arranged  in  definite  groups,  and  performs  a  physio- 
logic function.     These  groups  are  the  secretory  units  of  the  organ. 

Glands  may  be  classified  in  several  ways:  (i)  as  to  structure 
(2)  as  to  secretion  and  (3)  as  to  outlet. 

1.  Structure. — As  the  secretory  units  are  of  different  shapes  we 
have  the  following  divisions  and  subdivisions: 

Tubular  Glands. 
Simple. 
Branched. 
Coiled. 
Compound. 

Tubulo-alveolar  Glands. 

Alveolar,  or  Racemose  Glands. 
Simple. 
Compound. 

Tubular. — Simple  tubular  glands  are  mere  cylindric  depressions 
in  the  mucous  membrane.  They  are  lined,  usually,  by  simple 
columnar  cells.  These  rest  upon  a  delicate  basement  membrane 
and  this  is  supported  by  the  tunica  propria  of  the  mucous  membrane. 
In  the  stomach  the  cells  are  acid,  peptic  and  some  goblet  cells;  in 
the  small  intestine  the  goblet  cells  predominate  near  the  outlet 
while  the  remainder  of  the  gland  is  lined  with  simple  columnar 
elements.  At  the  fundus  of  the  glands  there  are  certain  cells  with 
granular  protoplasm;  in  some  of  these  cells  the  granules  are  acido- 
philic and  in  others  basophilic.  Each  gland  consists  of  a  fundus, 
neck  and  mouth. 

Simple  tubular  glands  are  found  in  the  cardiac  end  of  the  stomach 
and  in  the  small  and  large  intestines. 

The  branched  tubular  are  like  the  above,  except  that  the  blind 
end  consists  of  two  or  more  secretory  units.  Each  secretory  unit 
consists  of  a  fundus  and  neck  and  the  single  outlet  for  all  represents 


GLANDS 


93 


the  mouth.  The  lining  cells  may  be  columnar,  or  ciliated,  as  in 
the  uterus.  These  glands  are  found  in  the  fundus  and  pyloric 
portion  of  the  stomach,  in  the  duodenum  (Brunner's  glands)  in, 
the  uterus,  and  in  the  prostate. 


Fig.  51. — Gland  of  Lieberkuehm  from  a  Section  of  the  Large 

Intestine. 
a.    Lumen;    b,  secretion  of  cells;  c,   nucleus  and  cytoplasm  of  cell;  d,  fundus 
cells  at  the  beginning  of  secretion;  e,  f,  goblet  cells  in  later  stage;  g,  dying 
goblet  cells.      (Stohr's  Histology.) 

Coiled  tubular  glands  are  really  simple  tubes,  the  secretory  por- 
tion of  which  has  become  coiled  and  convoluted  to  occupy  as  small 
a  space  as  possible.     The  lining  cells  are  columnar  or  cuboidal 


94 


PRACTICAL  HISTOLOGY 


(low  columnar).  These  rest  upon  a  basement  membrane  which  is 
further  supported  by  areolar  tissue  for  the  capillaries  and  nerves. 
Around  the  outside  is  a  capsule  that  delimits  the  organ  from  the 
surrounding  tissues. 

Examples  of  this  variety  are  the  sweat  and  ceruminous  glands. 


Fig.  52. — Diagrams  of  Tubular  Glands. 

A,  Simple  tubular.   B,  coiled  tubular.   C,  branched  tubular.   D,  compound  tubular. 

(Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 

Compound  tubular  glands  are  those  in  which  the  primitive 
tubules  have  divided  and  redivided  until  an  enormous  number  of 
divisions  has  resulted.  Pure  examples  of  this  variety  are  the  liver 
(also  called  reticular),  testicle,  kidney,  thyreoid,  lacrimal  and  ser- 
ous glands  of  the  mucous  membranes. 


GLANDS  95 

A  compound  gland  is  surrounded  by  a  capsule  of  white  fibrous 
connective  tissue  that  sends  in  septa  that  divide  the  gland  into 
lobes.  These  are  further  subdivided  by  smaller  septa  into  lobules, 
the  structural  units  of  the  gland.  Within  the  lobule  is  a  delicate 
reticulum  that  forms  the  supportive  tissue  of  the  blood-vessels, 
nerves,  lymph  channels  and  epithelium.  This  constitutes  the 
interstitial  tissue.  The  epithelium,  or  functionating  part,  con- 
stitutes the  parenchyma.  In  the  lobule  a  single  layer  of  epithelial 
cells  rests  upon  a  basement  membrane;  these  cells  are  arranged  in 
the  form  of  tubules  or  saccules  and  represent  the  secretory  units 
of  the  gland.  The  cavity  or  lumen  in  the  center  of  each  tubule 
leads  into  an  intralobular  duct  that  connects  directly  with  the  units. 
These  ducts  are  lined  with  low  epithelial  cells  that  rest  upon  a 
basement  membrane  supported  by  areolar  tissue.  These  ducts 
unite  to  form  larger  ducts;  the  latter  and  the  larger  vessels  lie  in 
the  interlobular  tissue.  The  interlobular  ducts  unite  to  form 
larger  ducts  that  ultimately  form  the  single  excretory  duct  of  the 
gland. 

The  arteries  usually  enter  at  one  region,  the  hilus  of  the  organ. 
They  then  divide  into  branches  that  follow  the  larger  septa  and 
into  branches  that  lie  in  the  interlobular  connective  tissue.  From 
these  interlobular  vessels  branches  ramify  the  lobules  and  form  a 
plexus  around  the  tubules  and  acini.  The  venous  channels  arise 
from  this  plexus  and  have  a  course  corresponding  to  that  of  the 
arterial  vessels  and  form  usually  one  vein  that  leaves  at  the  hilus. 
As  the  tissue  spaces  around  the  tubules  and  acini  are  very  numerous 
the  plasma  of  the  blood  transudes  into  these  and  bathes  the  cells 
with  nutrient  material  and  into  this  lymph  the  effete  materials  are 
also  passed  from  the  cells.  In  the  case  of  glands  with  sinusoidal 
capillaries  (liver,  adrenal,  etc.)  there  are  very  few  tissue  spaces 
and  the  capillaries  penetrate  between  the  epithelial  cells  and  lie  in 
direct  contact  wTith  them.  Vessels  also  supply  the  ducts  and  frame- 
work of  the  organ. 

The  lymph  gradually  passes  into  definite  vessels  (capillaries) 
and  then  into  larger  channels  and  is  then  collected  into  one  or 
several  vessels  which  leave  at  the  hilus  and  capsular  region  (deep 
and  superficial  lymphatics). 


96  PRACTICAL   HISTOLOGY 

The  nerves  of  glands  are  for  the  vessels  and  for  the  epithelial 
cells.  Those  for  the  vessels  are  vasodilators  and  vasoconstrictors. 
By  the  action  of  the  former  the  blood  supply  is  increased  and  there- 
fore the  secretion  also;  the  latter  have  the  reverse  action.  In  some 
instances  the  vasodilators  are  derived  from  the  sympathetic  nerves 
and  in  others  from  the  cerebrospinal  nerves  through  the  sympathetic 
plexuses.  The  vasoconstrictors  usually  arise  from  the  sympathetic 
nerves.  The  nerves  to  the  epithelial  cells  are  of  two  varieties, 
trophic  and  secretor.  The  trophic  nerves  seem  to  accompany 
the  vasoconstrictors  and  by  their  action  cause  an  increase  in  the 
secretion  products  within  the  cells.  The  secretor  fibers  seem  to 
accompany  the  vasodilators  and  produce  a  rapid  discharge  of  the 
secretion. 

A  compound  tubular  gland  may  be  compared  to  a  bunch  of 
tokay  grapes,  the  grapes  representing  the  secretory  units  and  the 
various  stems  the  ducts.  A  full  bunch  of  these  grapes  will  show 
the  small  groups  of  grapes  forming  larger  groups  and  these  can 
readily  be  likened  unto  the  lobules  and  lobes  of  a  gland;  the  various 
stems  represent,  excellently,  the  various  ducts,  intralobular,  inter- 
lobular, interlobar  and  main  ducts.  The  spaces  between  the  various 
groups  and  individual  grapes  constitute  the  region  of  the  inter- 
stitial connective  tissue  supporting  blood-vessels,  nerves  and  lymph 
channels. 

Tubulo-alveolar  glands  are  those  in  which  the  terminal  tubules 
possess  sac-like  evaginations  along  the  walls.  Such  are  the  sub- 
maxillary, sublingual,  mammary  glands  and  the  lungs. 

The  general  structure  of  these  glands  is  like  the  preceding.  A 
tubulo-alveolar  gland  may  be  likened  unto  a  bunch  of  mixed  grapes, 
some  of  the  tokay  variety  and  some  of  the  ordinary  round,  or 
concord  variety.  Both  varieties  may  be  found  in  the  same  lobules, 
or  whole  lobules,  or  lobes  may  consist  of  just  one  form. 

Alveolar. — The  simple  alveolar,  or  saccular,  glands  are  sac-like 
depressions  extending  from  the  free  surface.  They  are  compara- 
tively few  in  number,  and  occur  as  the  smallest  sebaceous  glands. 

Each  consists  of  a  sac-like  structure  connected  to  the  epithelial 
surface  by  a  slender  neck,  or  duct.  The  sac  instead  of  being  lined 
with  a  single  layer  of  epithelial  cells,  as  in  all  of  the  preceding  forms, 


GLANDS 


97 


is  filled  with  a  solid  mass  of  very  large  polyhedral  cells.  Those 
cells  nearest  the  duct  show  signs  of  degeneration  and  fatty  changes; 
ultimately  they  disintegrate  entirely  and  the  thick,  fatty  substance 
constitutes  the  secretion  (sebum).  These  cells  in  forming  the 
secretion  die.  In  other  glands  the  secreting  cells  form  secretion 
over  and  over  and  live  for  a  considerable  time.  In  sebaceous 
glands  the  disintegrated  cells  are  rapidly  replaced  by  mitosis  of  the 


Fig.  53. — Diagrams  of  Alveolar  Glands. 
A,    Tubulo-alveolar;  B,    simple    alveolar;    C,    compound    alveolar. 
Reference  Handbook  of  the  Medical  Sciences.) 


(Radasch, 


cells  toward  the  basement  membrane.  Outside  of  the  basement 
membrane  is  a  tunica  propria  for  the  support  of  blood-vessels, 
nerves  and  lymph  channels.  The  peripheral  portion  of  this  is 
condensed  to  form  a  capsule. 

The  compound  racemose  glands  are  like  the  compound  tubular, 
except  that  the  terminal  portions  are  saccular,  instead  of  tubular. 
Such  glands  are  the  pancreas,  parotid,  and  the  large  sebaceous 
glands. 


98  PRACTICAL  HISTOLOGY 

The  secreting  units  of  the  large  sebaceous  glands,  like  in  the 
simple  form,  are  filled  with  a  solid  mass  of  epithelium  and  the 
changes  here  are  the  same  as  in  the  simple  glands. 

2.  Secretion. — The  function  of  a  gland  is  to  give  rise  to  a  sub- 
stance to  be  used  by  the  body  in  some  of  its  many  processes  or 
to  remove  waste  products  (excretions).  The  former  substance  is 
called  a  secretion,  and  it  may  be  liquid  or  cellular  (ovum).  The 
liquid  secretions  may  be  serous,  mucous,  or  mixed.  These  terms, 
applied  to  the  respective  glands  as  well,  have  reference  to  the 
salivary  glands  alone. 

Serous  glands  are  those  which  form  a  thin  albuminous  secretion. 
The  glandular  cells  respond  well  to  stains.  The  parotid  and  pan- 
creas belong  to  this  class. 

The  appearance  of  these  glands  differs  when  they  are  in  a  state 
of  activity  or  of  rest.  At  the  beginning  of  the  stage  of  rest  the  cells 
are  comparatively  small  and  shrunken  and  the  lumen  of  each 
acinus  is  large.  The  nucleus  is  centrally  placed  and  the  cytoplasm 
is  devoid  of  secretion  granules.  As  the  secretion  is  formed  the 
cytoplasm  changes  in  appearance  to  either  clear  or  granular  accord- 
ing to  the  gland.  In  the  sweat  glands  the  cytoplasm  is  clear  as 
the  secretion  is  essentially  watery,  while  in  the  pancreas  and  parotid 
glands  the  cytoplasm  is  granular.  In  the  latter  glands  the  secre- 
tion is  zygomotic  in  character,  hence  the  difference.  As  the  secre- 
tion increases  the  nucleus  is  forced  toward  the  basal  extremity  of 
the  cell  and  the  secretion  lies  toward  the  lumen  end,  so  that  ulti- 
mately the  cell  has  a  swollen  appearance  and  the  lumen  is  occluded 
or  nearly  so. 

During  the  stage  of  secretory  activity  the  secretion  is  passed  into 
the  lumen  of  the  acinus  and  the  cell  is  smaller  and  shrunken.  The 
cytoplasm  is  finely  granular,  if  the  secretion  has  been  watery  and 
if  the  secretion  has  been  granular  the  cytoplasm  is  clear. 

In  many  serous  gland  cells  secretory  caniliculi  have  been  demon- 
strated. These  may  open  into  the  lumen  of  the  tubules  or  into 
the  lymph  spaces  or  blood-vessels.  Some  of  these  channels  are 
in  the  nature  of  nutrient  canals,  however.  Serous  glands  stain 
darkly  with  the  ordinary  stains. 
Mucous  glands  are  those  that  give  rise  to  a  thick  viscid  substance. 


GLANDS  99 

The  cells  here  stain  but  lightly  with  the  ordinary  stains.  Such 
are  the  small  glands  found  in  the  mouth,  esophagus,  trachea  and  the 
sublingual  gland,  according  to  some  writers. 

The  cytoplasm  of  the  cells  of  the  mucin  secreting  glands  is  finely 
granular,  the  nucleus  centrally  located,  the  cells  smaller  and  the 
lumen  comparatively  large,  during  the  stage  of  rest.  The  granules 
lie  in  the  lumen  end  of  the  cells,  increase  rapidly  in  size  and,  after 
prolonged  rest,  occupy  over  half  of  the  thickness  of  the  cells.  The 
granules  are  much  larger  than  those  of  the  serous  glands  and  respond 
to  the  special  stains  for  mucin.  As  these  granules  increase  in  num- 
ber and  size  the  cells  become  swollen  and  the  nuclei  and  cytoplasm 
are  forced  toward  the  basement  membrane  and  the  lumen  is  practi- 
cally occluded.  In  the  stage  of  secretion,  by  the  contraction  of  the 
cells  or  by  the  transudation  of  water  through  them  (from  the  blood 
or  lymph),  the  granules  become  swollen,  dissolve  and  form  a 
homogeneous  mass  which  is  passed  from  the  cell.  The  cell  then  is 
somewhat  shrunken  and  the  area  formerly  occupied  by  the  secretion 
shows  a  delicate  reticulum  in  which  the  new  globules  of  secretion 
form.  The  presecretion  globules  are  called  mitcinogen  and  the 
finished  product  mucin  and  they  usually  behave  differently  to  stains. 
The  secretion  granules  of  the  various  glands  are  probably  mito- 
chondrial in  origin.  In  most  glands  the  extrusion  of  the  secretion 
is  caused  by  the  action  of  the  nerve  system  or  by  hormones  in  the 
blood. 

The  cells  of  mucin-secreting  glands  stain  lightly  in  contrast  to  the 
cells  of  the  serous  glands.  This  is  due  to  the  fact  that  the  granules  in 
the  serous  cells  are  not  readily  soluble  in  the  aqueous  or  alcoholic 
fixing  agents  so  that  they  remain  and  are  stained.  On  the  other 
hand  the  secretion  globules  or  granules  of  the  mucin  cells  are  readily 
swollen  or  dissolved  by  water  or  even  alcohol  so  that  in  fixed  cells 
they  were  for  a  long  time  unobserved.  This  action  is  produced  even 
by  normal  salt  solution  and  serum.  They  may  readily  be  seen  in 
fresh  tissue  examined  in  a  2  to  5  per  cent,  sodium  chlorid  solution. 
If  the  tissue  be  fixed  in  osmic  acid  vapor,  or  in  a  mixture  of  equal 
parts  of  osmic  acid  (5  per  cent,  in  3  per  cent,  sodium  chlorid)  and 
saturated  solution  of  potassium  bichromate,  the  granules  are  un- 
dissolved and  readily  found. 


100  PRACTICAL   HISTOLOGY 

Mucin  responds  to  special  stains,  muchematein  and  mucicarm'ui. 
In  the  fresh  state  it  is  clear,  slimy  and  of  a  pearly  white  color.  Al- 
cohol coagulates  it  forming  a  heavy,  white,  stringy  precipitate. 
It  does  not  respond  well  to  the  ordinary  stains  so  the  part  of  the  cells 
containing  it  looks  unstained  in  the  ordinary  technic. 

In  most  mucous  glands  groups  of  darkly  staining  cells  are  seen  in 
the  bases  of  tubules.  These  cells  contain  a  finely  granular  cyto- 
plasm and  are  arranged  in  cresentic  groups  called  the  crescents  of 
Gianuzzi,  or  the  demilunes  of  Heidenhain.  These  cells  and  groups 
vary  in  size  in  the  different  glands.  Some  consider  them  the  resting 
stages  of  the  mucin-secreting  elements  and  others  consider  them  as 
entirely  different  and  independent  structures.  It  seems  that  they 
are  a  form  of  serous  cell.  The  cytoplasm  always  responds  well  to 
the  plasmatic  stains  and  also  contains  secretory  canaliculi  that 
empty  the  secretion  into  a  canalicular  system  between  the  cells  of 
a  group.  From  this  system  the  secretion  is  ultimately  passed  into 
the  lumen  of  the  tubule.  From  this  it  would  appear  that  the  so- 
called  pure  mucous  glands  are  really  mixed  glands  in  that  they 
contain  the  demilunes. 

Mixed  glands  are  those  in  which  both  varieties  of  secretion  are 
formed.  The  secretory  areas  are  stained  darkly  or  lightly,  accord- 
ing to  whether  they  are  serous  or  mucous.  The  sublingual  and  sub- 
maxillary glands  are  examples,  and  of  these,  the  latter  is  the  more 
characteristic. 

The  minute  structure  of  these  glands  will  be  considered  under  the 
Alimentary  Tract. 

The  excretory  glands  are  the  kidneys,  lungs  and  sweat  glands. 
Each  will  be  considered  in  detail,  under  its  respective  system. 

3.  Outlet. — As  a  rule,  all  glands,  at  some  period  in  their  develop- 
ment, are  connected  with  the  mucous  surface  by  a  tube  called  a  duct. 
This  connection,  in  most  instances,  persists,  but  where  it  disappears, 
or  where  it  never  occurred,  the  gland  becomes  isolated,  and  the  term 
ductless  gland  is  applied.  Such  are  the  adrenals,  hypophysis  and 
thyreoid  bodies,  parathyreoid,  carotid  and  coccygeal  glands,  cer- 
tain areas  of  the  ovary  and  testis  and  the  areas  of  Langerhans  of  the 
pancreas.  The  cells  are  arranged  in  the  form  of  solid  cords,  tubules 
and   even  alveoli.     The  delicate   reticulum    supporting   these   cells 


GLANDS  ioi 

usually  contains  capillaries  of  the  sinusoidal  type,  that  is,  the  epi- 
thelium and  the  endothelium  are  in  contact  with  each  other  and 
lymph  spaces  are  not  numerous  or  are  absent.  In  some  instances 
the  lymphatics  have  a  similar  arrangement  so  that  the  internal  secre- 
tion is  passed  directly  to  the  blood  or  lymph  vessels.  In  the  liver 
the  secretory  capillaries  of  the  cells  are  said  to  communicate  with 
the  sinusoid  thereby  emptying  the  urea  formed  here  directly  into 
the  vascular  system. 

The  glands  with  ducts  pour  their  secretions,  or  excretions,  into 
the  various  tracts  with  which  they  are  connected. 


CHAPTER  IV 
CONNECTIVE  TISSUES 

The  connective  tissues  are  the  supportive  tissues  of  the  body. 
They  are  characterized  by  the  predominance  of  the  intercellular 
substance  over  the  cellular  elements.  The  intercellular  substance 
varies  in  consistency  from  the  liquor  sanguinis  of  the  blood  and  the 
soft  fibrous  material  of  areolar  and  elastic  tissues  to  the  harder 
cartilage,  bone  and  dentin.  This  variation  is  due  to  the  function 
performed.  Although  there  are  many  varieties  they  are  all  derived 
from  the  same  embryonic  type,  mesenchyme,  and  change  as  they 
progress  in  their  development.  Even  in  their  adult  forms  some  show 
their  close  relationship  to  one  another  and  while  some  may  be  looked 
upon  as  different  stages  of  the  young  type  others  are  distinct  modifi- 
cations, as  cartilage,  bone  and  dentin.  The  cellular  elements  re- 
semble one  another  somewhat  in  the  different  varieties,  are  compara- 
tively few  in  number  and  are  arranged  singly  or  in  small  groups  in 
the  intercellular  substance.  This  matrix  or  ground  substance  pre- 
dominates and  it  is  the  variation  of  this  that  gives  us  the  different 
varieties  of  connective  tissue.  They  often  replace  one  another. 
The  ground  substance  and  the  fibers  are  stained  by  the  silver  nitrate 
method  showing  the  numerous  lymph  spaces  existing  in  most 
varieties.  The  vascularity  also  varies,  some  forms  having  few 
vessels  while  others  are  quite  vascular.  The  connective  tissues 
form  the  framework  and  supportive  substance  of  the  various  organs 
and  the  body  in  general  and  fill  up  what  ordinarily  would  be  spaces. 

In  the  formation  of  these  tissues  the  fibroblasts  of  the  mesenchyme 
reproduce  rapidly  and  secrete  a  semi-solid  intercellular  substance. 
With  the  fusion  of  the  fibroblasts  a  syncytial  structure  is  formed. 
The  cytoplasm  around  the  nuclei  soon  differentiates  into  endoplasm 
and  exoplasm  and  in  the  latter  the  mitochondria  are  said  to  form 
the  fibrils  at  the  expense  of  the  endoplasm.     The  remainder  of  these 

I02 


CONNECTIVE   TISSUES 


I03 


little  masses  of  again  isolated  cytoplasm  constitute  the  connective- 
tissue  cells.  The  fibers  are  of  three  types,  white,  elastic  and  reticular. 
Additional  fibers  are  said  to  be  formed  by  the  splitting  of  these. 

For  the  convenience  of  description,  the  connective  tissues  have 
been  subdivided  into  the  following  varieties: 


Fibrous. 

Mod 

ified. 

1.  Areolar. 

6. 

Adipose. 

2.  White  fibrous. 

7- 

Lymphoid. 

3.  Yellow  elastic. 

8. 

Cartilage 

4.  Mucous. 

9- 

Bone. 

5.  Retiform. 

10. 

Dentin. 

11.  Blood. 

Fig.  54. — Areolar  Tissue. 

a,  Lamellar  cell;  b,  bundles  of  white  fibers;  c,  plasma  cells;  d,  elastic  fibers;  e, 
clasmocytes;  /,  granule  cells.  (Radasch,  Reference  Handbook  of  the  Medical 
Sciences.) 

i.  Areolar  tissue  is  a  delicate,  web-like  form  representing  the  most 
widely  distributed  variety.  It  consists  of  an  interlacement  of  white 
and  yellow  elastic  fibers  containing  various  cellular  elements.  The 
spaces  thus  formed  permit  of  a  wide  diffusion  of  lymph  over  a  great 


104  PRACTICAL   HISTOLOGY 

distance.  This  variety  is  found  binding  the  skin  to  the  fascia  be- 
neath, as  the  intermuscular  septa,  surrounding  blood-vessels,  nerves 
and  lymph  channels  and  assists  in  the  formation  of  most  of  the 
organs  of  the  body  (tunica  propria,  submucosa,  interstitial  tissue 
of  glands  and  gland-like  organs). 

The  cellular  elements  are  lamellar  cells,  clasmocytes,  plasma 
cells,  wandering  cells  and  mast  cells. 

i.  The  lamellar  cells  are  the  chief  cells  and  are  usually  flattened, 
stellate  elements.  Their  processes  may  anastomose  with  those  of 
other  cells.  The  cytoplasm  is  usually  clear,  but  a  few  granules  may 
be  present.  The  nucleus  is  oval  and  stains  readily.  The  youngest 
cells  are  round;  these  become  spindle-shaped  by  the  development  of 
several  processes  and  by  the  formation  of  more  processes  become 
stellate  in  form.  They  may  be  pigmented  as  in  the  eyeball.  In  the 
lymphatic  spaces  the  lamellar  cells  are  flattened  elements  that  con- 
stitute the  endothelial  cells. 

2.  The  clasmocytes  are  irregular,  elongated  elements  that  are 
probably  derived  from  the  wandering  cells.  The  cytoplasm  is 
granular  and  may  contain  vacuoles.  The  nucleus  is  large  and  oval 
in  form. 

3.  The  plasma  cells  are  flattened,  elongated,  or  spheroidal  ele- 
ments that  may  possess  branches;  the  cytoplasm  contains  some 
vacuoles  and  a  number  of  basophilic  granules.  The  nucleus  is 
usually  small  and  eccentrically  placed.  These  cells  are  most  numer- 
ous in  the  blood-forming  and  lymphoid  organs. 

4.  The  wandering  cells  are  merely  leukocytes  that  have  wandered 
in  from  the  blood  or  lymph. 

5.  Mast  cells  are  large,  round  elements  in  which  the  cytoplasm 
contains  a  large  number  of  basophilic  granules.  These  cells  are 
found  chiefly  in  bone-marrow  and  regions  where  fat  is  being  depos- 
ited.    They  are  probably  modified  leukocytes. 

Pigment  cells  are  seen  in  the  iris,  choroid  and  derma  and  represent 
a  protection  against  light.  These  are  really  lamellar  cells  in  which 
the  pigment  granules  are  collected  in  the  cytoplasm.  This  sub- 
stance may  be  melanin,  hemaglobin  or  fat  pigments  (lipochromes). 
The  pigment  cells  of  the  derma  may  have  ameboid  power  to  a  slight 
degree.     In  the  skin  of  the  frog  this  pigment  is  abundant  in  the 


CONNECTIVE    TISSUES 


TO: 


stellate  cells  and  the  color  of  the  skin  can  be  varied  by  the  distribu- 
tion thereof.  When  the  pigment  granules  are  forced  out  of  a  fresh 
cell  these  granules  exhibit  "Brownian  motion." 

The  intercellular  substance  is  soft  and  fibrillar  in  character.  The 
white  fibers  consist  of  delicate  bundles  of  fibrils  that  pass  from  one 
bundle  to  another.  The  fibers  run  in  wavy  bundles  that  interlace 
with  one  another  and  with  the  elastic  fibers.     The  elastic  libers  are 


Fig.  55. — Pigmented  Connective  Tissue  Cells  From  the  Web  ok  a  Frog's 
Foot.     (Photographed,  Obj.  16  mm.,  oc.  10  X.) 

yellow  in  color  and  branch.  They  are  not  arranged  in  bundles  and 
are  usually  thicker  than  the  white  fibers. 

2.  White  fibrous  tissue  is  that  variety  in  which  the  bundles  do  not 
interlace  but  run  parallel  to  one  another.  It  is  white,  shiny,  tough 
and  yet  pliable.  It  is  found  as  the  ligaments,  jascice,  dura  and 
tendons. 

In  fascia,  or  aponeuroses  the  fiber  bundles  are  arranged  in  layers 
that  run  transversely  and  longitudinally.  The  bundles  of  each 
layer  are  parallel  to  one  another  and  do  not  interlace.  In  the 
dura  they  take  different  directions  and  decussate  with  one  another, 
forming  a  dense  unyielding  membrane. 

Tendons   are  dense  white  fibrous  tissues,  in  which  all  the  fiber 


io6 


PRACTICAL  HISTOLOGY 


6     d. 


ft    a 


&  a       c&     da 


Fig.  56. 
-Mucous  Connective  Tissue,  a,  Spindle  cells;  b,  stellate  cell;  c,  inter- 
cellular substance.  B. — Cross-section  of  Tendon,  o,  Epitendineum; 
b,  peritendineum;  c,  tendon  fasciculi;  d,  interfascicular  space.  C. — Part 
of  B,  highly  magnified,  a,  Epitendineum;  b,  cell  in  a;  c,  peritendineum; 
d,  tendon  fasciculus;  e,  interfascicular  space.  D. — Tendon  Cells  from 
Interfascicular  Spaces.  E. — Elastic  Tissue,  Cross-section  of  Ligamentum 
Nuchae.  a,  Elastic  fibers;  b,  white  fibrous  supportive  tissue.  F. — E 
highly  magnified,  a,  Elastic  fibers;  b,  white  fibrous  supportive  tissue, 
G. — Areolar  Tissue,  a,  White  fiber  bundles;  b,  elastic  fibers;  c,  spindle 
cell;  d,  granule  cell;  e,  plasma  cell;  /,  stellate  cell.  H. — Adipose  Tissue, 
a,  Interlobular  connective  tissue;  b,  fat  cells;  c,  nucleus  and  cytoplasm 
and  of  the  cell.  I. — H.  highly  magnified,  a,  Fat  cell;  b,  cytoplasm 
and  nucleus  of  cell.  K. — Lymphoid  Tissue,  a,  Leukocytes;  b,  stellate 
connective  tissue  cells;  c,  reticulum.  L. — Pigmented  Connective  Tissue 
Cell  from  a  Pike. 


CONNECTIVE   TISSUES 


107 


bundles  have  a  parallel  course.  The  whole  structure  is  surrounded 
by  a  sheath  of  looser  tissue,  called  the  epitendineum,  from  the  inner 
surface  of  which  septa  are  sent  in  that  divide  the  tendon  fibers  into 
large  secondary  bundles.  These  latter  are  further  subdivided  into 
primary  bundles,  each  of  which  is  surrounded  by  a  minute  sheath, 
the  peritendineum.  In  these  sheaths  or  septa  are  found  the  blood- 
vessels, nerves  and  lymph  channels  of  the  tendon.  Although  the 
bundles  run  parallel  to  one  another  they  receive  slips  from  and  give 
off  slips  to  neighboring  bundles.  Still  this  does  not  interfere  with 
the  important  operation  of  tendon-splicing  so  useful  in  surgery. 
Between  the  bundles  of  tendon  fibers  are  seen  the  peculiar  tendon 
cells.  These  are  lamellar  cells  that  are  arranged  in  rows  or  chains. 
These  cells  upon  surface  view  are  rectangular,  or  oblong  but  upon 
cross-section  they  are  stellate.  This  is  due  to  the  fact  that  they  are 
packed  in  between  the  bundles  and  have  become  moulded  by  these 


Fig.  57. — Tendon  Cells  Greatly  Magnified.     {Maximow  after  Tourneau.) 


into  their  peculiar  shape.  In  denser  areolar  tissue  the  lamellar 
cells  may  have  the  same  form,  due  to  pressure.  The  cells  are  thicker 
in  the  middle  than  at  the  extremities;  the  nuclei  are  oval,  lightly 
stained  and  may  contain  one  or  two  nucleoli.  In  two  adjoining 
cells  they  will  be  seen  near  the  line  of  junction,  but  in  the  cells  on 
either  side  of  these,  they  are  separated  by  nearly  the  length  of  the 
two  cells.  These  cells  may  possess  fine  branches  that  pass  in  be- 
tween the  tendon  bundles.  The  surface  cells  of  many  tendons  and 
aponeuroses  may  form  a  continuous  layer  and  their  irregular  outlines 
may  be  brought  out  with  silver  nitrate. 


108  PRACTICAL   HISTOLOGY 

A  few  elastic  fibers  may  be  found  between  the  larger  bundles  of 
tendon  fibers.  A  tendon  is  very  tough  and  strong  and  is  broken  with 
difficulty.     Its  strength  is  greater  than  a  bone  of  equal  diameter. 

White  fibrous  tissue  yields  gelatin  (collagen)  upon  boiling.  The 
fibers  digest  in  gastric  juice  and  swell  when  treated  with  dilute  acids. 
The  fibers  do  not  dissolve  readily  when  placed  in  pancreatin.  Picro- 
fuchsin  is  a  special  stain  for  this  variety. 

2.  Elastic  tissue,  as  its  name  indicates,  has  the  peculiar  property  of 
elasticity.  The  cellular  elements  are  comparatively  few  and  of  the 
lamellar  variety. 

The  fibers  are  yellow  in  color,  refractile,  and  coarser  than  those  of 
the  white  variety,  averaging  from  i  to  15  microms  in  diameter.  It 
is  one  of  the  components  of  areolar  tissue  where  the  fibers  branch. 
In  other  places  it  is  found  in  the  form  of  ligaments  and  in  the  blood- 
vessels it  may  form  a  membrane.  According  to  Mall  each  fiber 
consists  of  a  delicate  sheath  surrounding  the  elastic  substance;  the 
latter  stains  deeply  with  magenta.  In  lower  animals  (quadrupeds) 
it  plays  an  important  part  as  the  ligamentum  nuchae  which  supports 
the  head.  In  this  ligament  the  fibers  are  very  heavy  and  are  bound 
into  smaller  and  larger  bundles  by  white  fibrous  tissue.  In  the  larger 
quadrupeds  elastic  tissue  forms  an  important  subcutaneous  fascia 
that  assists  in  supporting  the  contents  of  the  abdomen. 

In  man  elastic  tissue  is  found  in  the  ligamenta  subflava,  the  crico- 
thyreoid,  thyreohyoid  and  stylohyoid  ligaments,  in  the  vocal  cords 
and  as  longitudinal  bands  beneath  the  mucosa  of  the  trachea  and 
its  branches.  In  the  blood-vessels  it  is  found  as  individual  fibers 
or  in  the  form  of  Henle's  fenestrated  membrane. 

Elastic  tissue  is  digested  by  pancreatin  and  somewhat  by  pepsin; 
it  is  not  dissolved  by  acetic  acid.  Upon  boiling  it  yields  elastin. 
Special  stains  are  Weigert's  elastica  and  orcein  stains. 

White  fibrous  and  yellow  elastic  tissues  are  poorly  supplied  with 
blood-vessels  and  nerves  but  are  rich  in  lymphatics. 

The  origin  of  white  fibrous  and  yellow  elastic  tissues  is  still  un- 
settled. According  to  Meves  and  others  the  fibers  are  formed  within 
the  cell  by  the  direct  conversion  of  the  exoplasm  and  processes 
into  fibrillar.  According  to  Merkel  and  others  both  kinds  of  fibers 
are  formed  in  the  homogeneous  intercellular  substance  by  secre- 


CONNECTIVE    TISSUES 


I OQ 


lions  from  the  cells  and  not  by  the  direct  change  of  the  cytoplasm. 
Mall  regards  the  intercellular  matrix  as  exoplasm  and  the  cells  and 
processes  as  endoplasm.  He  regards  the  exoplasm  as  living  substance 
in  which  the  fibrillar  develop. 


c^H&Sb 


MM 

mam 


Fig.  58. — Elastic  Fibers.     (Lewis  and  Stohr.) 
A,    Network  of  thick  elastic  fibers  below,  passing  into  a  fenestrated  membrane 
above.     From  the  human  endocardium.     B,   Thick  elastic  fibers  (/)  from 
the  ligamentum  nucha?  of  the  ox;  b,  white  fibers.     C,    Cross-section  of  the 
ligamentum  nuchae,  lettered  as  in  B. 

Recently  it  has  been  found  that  fibrils  develop  in  organizing  blood 
clots,  directly  from  the  fibrin  without  the  assistance  or  intervention 
of  fibroblasts  or  leukocytes. 


110  PRACTICAL   HISTOLOGY 

3.  Mucous,  or  embryonic  connective  tissue  is  that  variety  in 
which  the  intercellular  substance  is  semi-fluid.  It  represents  the 
mesenchyme  that  differentiates  into  the  other  forms.  Some  con- 
sider these  as  two  distinct  forms,  the  embryonic  tissue  occurring  in 
the  fetus  and  during  regeneration  of  connective  tissue  and  in 
pathologic  neoplasms;  the  mucous  is  considered  a  fully  developed 
type  of  connective  tissue  occurring  in  the  vitreous  humor  of 
the  eyeball,  the  pulp  of  the  teeth  and  as  Wharton's  jelly  of  the 
umbilical  cord. 

The  cells  of  embryonic  connective  tissue  are  chiefly  of  the  spindle- 
shaped  type  though  round  and  stellate  elements  are  present.  The 
fibers  are  few  in  number  and  fine;  they  form  a  network  that  contains 
in  its  meshes  the  predominating  semi-solid  ground  substance. 

In  the  mucous  connective  tissue  the  cells  are  chiefly  of  the  branched 
lamellar  type;  in  the  umbilical  cord  these  cells  are  numerous  but  in 
the  vitreous  humor  they  are  few  in  number.  The  fibers  are  fairly 
numerous  in  the  umbilical  cord  and  form  lavers  around  the  large 
vessels.  In  the  vitreous  humor  the  fibers  are  less  numerous  and 
tend  to  form  a  delicate  network.  The  ground  substance  is  more 
gelatinous  than  in  the  embryonic  type  and  also  contains  mucin. 
Both  varieties  are  devoid  of  blood-vessels,  nerves  and  lymph 
channels. 

In  the  pulp  of  the  teeth  the  fibrils  are  most  numerous.  They  form 
a  meshwork  for  the  support  of  the  abundant  blood-vessels,  nerves 
and  lymph  channels  of  the  tooth.  The  cellular  elements  are  greatly 
modified,  those  most  important  being  arranged  upon  the  surface 
of  the  pulp  in  a  single  layer.  These  are  the  odontoblasts;  they  are 
flask-shaped  and  from  the  peripheral  surface  a  number  of  processes 
extend  into  the  dentinal  tubules.  Beneath  this  layer,  toward  the 
center  of  the  pulp  is  a  layer  of  irregular  cells  that  are  supposed  to  be 
converted  into  odontoblasts  as  these  are  needed. 

5.  Retiform  connective  tissues,  or  reticulum,  is  the  supportive 
tissue  of  glands  and  gland-like  organs.  According  to  Mall,  it  is  the 
least  differentiated  of  the  mesenchymal  tissues.  It  consists  of 
delicate  bundles  of  fibrils  forming  a  network,  in  the  meshes  of  which 
are  found  the  functionating  cells  of  the  organ.  The  cells  are  chiefly 
flattened  elements  that  clasp  the  bundles.     Recent  investigation 


CONNECTIVE  TISSUES 


III 


seems  to  confirm  the  fact  that  reticulum  is  simply  a  special  arrange- 
ment of  white  fibrous  tissue. 

This  tissue  is  more  resistant  to  those  reagents  that  dissolve  the 
white  variety  (hydrochloric  acid  and  potassium  hydrate)  and  does 
not  yield  elastin  upon  boiling,  but  a  mixture  of  gelatin  and  reticulin, 
nor  is  it  digested  by  pancreatin.  Among  the  special  stains  for  this 
tissue  is  Mallory's  reticulum  stain. 

Modified. — In  these  varieties  of  connective  tissue,  the  inter- 
cellular substance  varies  from  liquid  (blood)  to  the  hard,  unyield- 
ing material  found  in  bone  and  dentin. 


Fig.  59. — Section  of  Adipose  Tissue.     (Photograph.    Obj.  16  mm.,  oc.  7 . 5  X.) 

The  cellular  elements  also  differ,  as  will  be  seen  when  each  variety 
is  discussed. 

6.  Adipose  tissue,  or  fat  tissue  is  white  fibrous  tissue,  in  which 
the  cells  have  become  repositories  for  fat  globules.  These  cells  are 
quite  numerous,  but  the  stellate  shape  is  lost.  It  represents  a 
storage  of  nutritious  material  as  well  as  a  protective  structure. 

The  minute  globules  unite  to  form  a  single  large  drop  that  distends 
the  delicate  cell-membrane.  By  this  coalescence,  the  cytoplasm 
and  nucleus  of  the  cell  are  forced  to  one  side,  and  are  seen  as  a  thin 
band,  or  crescent.  The  nucleus  may  contain  vacuoles.  Fat  is  sup- 
posed to  originate  from  peculiar  ovoid  granules  in  the  cytoplasm. 


112 


PRACTICAL   HISTOLOGY 


Fat  cells  are  spherical,  when  not  closely  packed,  as  the  fat  is  liquid 
at  the  body  temperature.  After  death,  mar  gar  in  crystals  are  seen 
in  the  cytoplasm.  The  cells  are  collected  into  groups  called 
lobules,  and  these  form  large  masses  called  lobes.  Blood-vessels, 
nerves  and  lymphatics  are  present  in  considerable  number.  The 
first  named  are  especially  numerous,  as  there  is  a  close  relation  be- 
tween fat  deposition  and  the  vascularity  of  the  part. 

According  to  some  writers,  fat  cells  are  specialized  connective  cells 
that  exist  in  no  other  form.  This  seems  doubtful,  however,  as  ex- 
periments have  shown  that  when  animals  are  starved,  the  spherical, 


Fig.  60. — Section  of  Osmicated  Adipose  Tissue.     The  fat  is  black  and  the 
fibrous  tissue  is  unstained.      (Photograph.      Obj.  16  mm.  oc.  7.5  X.) 


fat-containing  cells  return  to  the  stellate  form  as  the  fat  is  removed. 
When  this  removal  occurs  the  cytoplasm  increases,  is  peculiar  in 
appearance  and  does  not  respond  readily  to  the  usual  stains.  These 
cells  still  contain  a  few  droplets  of  fat  and  are  called  serous  fat  cells. 
From  this,  it  would  seem  that  these  cells  act  merely  as  storage  cells. 
When  adipose  tissue  is  studied,  after  ordinary  preparation, 
merely  a  network  of  fibers  and  cell  boundaries  is  seen.  These 
spaces  (fat  cells)  measure  from  40  to  80  microns  in  diameter.  This 
is  due  to  the  fact  that  the  fat  has  been  removed  by  the  alcohol 


CONNECTIVE    TISSUES  113 

leaving  the  insoluble  white  fibrous  supportive  tissue.  In  such 
sections,  the  nucleated  crescents  of  cytoplasm  are  readily  observ- 
able. In  sections  of  ostnicated  fat,  the  peripheral  cells  are  circular 
in  outline,  while  the  deeper  ones  are  irregular  and  black,  due  to  the 
action  of  the  osmic  acid,  which  is  a  characteristic  reagent  for  fat. 
Sudan  III,  also  used  as  a  test  for  fat,  stains  the  globules  dark  red 
while  cyanin  stains  it  blue. 

Adipose  tissue  is  found  widely  distributed  over  the  body  wherever 
areolar  tissue  is  found,  except  in  the  penis,  scrotum,  ear,  eyelid, 
lungs  and  cranial  cavity.  From  the  orbit  and  around  the  kidneys  it 
never  entirely  disappears,  though  death  be  due  to  starvation. 


Fig.  61. — Cells  from  the  Subcutaneous  Tissue  of  a  Rabbit  Showing  Vari- 
ous Stages  of  Fat  Formation.     {After  Jordan  and  Ferguson.) 

According  to  E.  F.  Bell  the  deposition  of  fat  is  preceded  by  the 
appearance  of  a  peculiar  open  network  in  the  areolar  tissue.  This  he 
calls  "preadipose  tissue."  As  fat  is  being  deposited  a  rich  capillary 
plexus  develops. 

According  to  some  investigators  the  formation  of  fat  is  due  to  cer- 
tain ovoid  granular  cells  that  are  always  seen  in  the  areas  of  fat 
deposition.  It  has  also  been  shown  that  fat  cells  can  be  formed  by 
endothelial  cells  enclosing  free  globules  of  fat. 

The  first  appearance  of  fat  is  in  the  form  of  very  fine  granules  that 
are  derived  from  the  mitochondria  through  segmentation.  These 
segments  pass  through  the  nuclear  membrane  in  the  form  of  spherical 
granules,  elongate  and  segment  into  secondary  granules.  These 
granules  then  liquefy  and  coalesce  into  fat  droplets 


U4 


PRACTICAL  HISTOLOGY 


7.  Lymphoid  tissue  is  a  special  form  of  the  connective  variety 
consisting  of  a  network  of  reticulum,  in  the  meshes  of  which  are 
found  leukocytes,  or  white  blood-cells. 

These  cells  are  usually  the  small  lymphocytes,  although  varying 
numbers  of  the  large  lymphocytes  [hyalin  cells)  and  polyniiclear  cells 
are  to  be  seen.     For  a  description  of  these  cells,  see  Blood. 


Fig.  62. — Section  of  the  Mucosa  of  the  Jejunum  of  the  Cat. 
a,  Simple  columnar  and  goblet  cell  layer  separated  from  the  core  of  the  villus  b; 
the  latter  is  filled  with  diffuse  lymphoid  tissue,     c,  Simple  tubular  glands 
with  the  intervening  tunica  propria  filled  with   diffuse  lymphoid  tissue. 
(Photograph.     Obj.  16  mm.  oc.  7.5  X.) 


For  readiness  of  comprehension,  lymphoid  tissue  is  divided  into 
four  varieties:  (a)  diffuse;  (b)  solitary  nodule;  (c)  Peyer's  patch,  or 
agminated  nodule ;  and  (d)  lymph  node. 

(a)  Diffuse  lymphoid  tissue  is  an  indefinite  collection  of  leuko- 
cytes in  an  organ.  The  cells  are  not  especially  arranged,  neither  is 
there  a  special  supportive  tissue  present,  as  in  the  next  two  varieties. 


CONNECTIVE   TISSUES 


115 


The  cells  may  be  so  numerous  as  to  hide  entirely  the  tunica  propria 
of  the  structure  or  the  reticulum  of  the  organ. 

It  is  found  in  the  tunica  propria  of  the  alimentary,  respiratory 
and  urinogenital  tracts,  and  the  cells  are  merely  scattered  between 
the  bundles  of  white  fibrous  tissue.  It  forms  the  medulla  of  the 
thymus  body,  and  the  bulk  of  the  tonsil  and  spleen,  and  is  transient 
in  character. 


Fig.  63. — Solitary  Nodule  of  the  Spleen  of  a  Monkey.  The  light  area  is 
the  germinal  center.  The  nodule  is  surrounded  by  diffuse  lymphoid  tissue. 
(Photograph.     Obj.  16  mm.,  oc.  7.5  X.) 

(b)  Solitary  nodules  are  small,  dense  collections  of  lymphocytes. 
The  supportive  tissue  is  said  to  be  reticulum,  the  meshes  of  which 
are  larger  in  the  germinal  center  than  at  the  periphery.  Blood- 
vessels are  inconspicuous;  although  the  outline  may  be  slightly 
irregular,  it  is  sharp.  Each  nodule  usually  shows  a  lighter  center 
in  which  the  cells  are  fewer  and  younger.  This  is  called  the  germinal 
center,  and  here  the  new  cells  are  formed  by  karyokinetic  division. 
As  the  new  cells  are  formed  the  excess  cells  are  crowded  to  the 
periphery  of  the  nodule,  forming  there  a  denser  mass  giving  this 
area  a  darker. appearance. 


n6 


PRACTICAL  HISTOLOGY 


Solitary  nodules  are  found  in  the  alimentary  and  respiratory 
tracts,  the  spleen  and  tonsil.  They,  like  the  diffuse  variety,  are 
transient  structures. 

(c)  A  Peyer's  patch  is  a  more  or  less  regular  collection  of  solitary 
nodules  sharply  outlined  from  the  surrounding  tissue  and  i  to  5 
cm.  long.  Each  patch  consists  of  ten  to  sixty  solitary  nodules, 
each  of  which  usually  shows  a  germinal  center. 

Each  nodule  may  be  partially  or  completely  surrounded  by  a 
thin  capsule  of  white  fibrous  tissue,  although  usually  the  nodules 
merge  more  or  less  into  one  another.  They  are  located  in  the  sub- 
mucosa  of  the  ileum  opposite  to  the  attachment  of  the  mesentery. 


*>  € 
' 


Fig.  64. — An  Agmixated  Nodule  of  the  Ileum  of  a  Cat. 
(Photograph.      Obj.   48  mm.) 


Some  state  that  they  are  also  found  in  the  jejunum.  The  long  axis 
is  directed  parallel  to  the  long  axis  of  the  bowel.  They  are  visible 
to  the  unaided  eye.  Although  they  are  said  to  be  limited  to  the 
submucosa,  more  commonly  they  are  seen  invading  the  mucosa, 
having  broken  through  the  muscularis  mucosae.  Usually  in  those 
areas,  where  the  nodules  approach  the  epithelial  surface,  the  glands 
are  absent.  At  the  edge  of  the  nodules  the  glands  are  seen  arranged 
in  the  form  of  a  circle.  Often  the  villi  over  such  an  area  are  like- 
wise absent. 

(d)  Lymph  nodes  (lymph  glands)  are  small,  bean-shaped  bodies 
interposed  in  the  pathways  of  the  lymphatic  vessels.  As  they  are 
closely  related  to  the  lymphatic  system,  their  structure  will  be 
there  considered. 


CONNECTIVE    TISSUES 


117 


CARTILAGE 

8.  Cartilage  is  a  firm  substance  that  is  elastic,  yields  to  pressure 
and  is  readily  cut  with  a  sharp  knife.  It  is  characterized  by  the 
presence  of  a  solid  intercellular  substance  and  the  cells  differ  ma- 
terially from  those  of  the  preceding  varieties  of  connective  tissue. 
Three  varieties  are  found  in  man:  hyalin,  white  fibrocartilage  and 
yellow  elastic.  The  general  structure  will  first  be  considered  under 
perichondrium,  cells  and  intercellular  substance. 

The  perichondrium  is  a  fibrous  sheath  that  surrounds  cartilage 
and  gives  rise  to  its  cellular  elements.  It  is  composed  of  white 
fibrous  tissue,  and  is  divided,  functionally,  into  two  parts.     This 


Fig.  65. — Reproduction  of  Cartilage  Cells.     {After  Schleicher.) 

division  is  not  apparent  under  the  microscope,  as  the  layers  merge 
into  each  other.  The  outer  part  is  the  fibrous  layer,  and  contains 
few  cells.  The  inner  portion,  or  chondro  genetic  layer,  is  rich  in  cells 
that  are  not  of  the  stellate  type,  but  flattened  and  elongated,  or 
spindle-shaped.  These  are  the  chondroblasts,  which  become  cartilage 
cells.  Some  blood-vessels  also  are  present.  Bundles  of  fibers  from 
the  perichondrium  pass  into  the  matrix. 

The  cartilage  cells,  or  chondroblasts,  vary  in  the  different  portions 
of  the  cartilage.  Just  beneath  the  perichondrium,  they  are  flat 
and  thin,  indicating  an  early  stage.  Toward  the  center,  they 
gradually  become  broader  until,  finally,  they  are  oval  or  round  in 
form.  Each  cell  is  rich  in  cytoplasm,  which  contains  one  or  more 
vacuoles,  often  glycogen  and  occasionally  fat  droplets.  The 
nucleus  is  spheroidal,  appears  granular  and  may  contain  one  or 


n8 


PRACTICAL   HISTOLOGY 


more  nucleoli.  Each  cell  lies  in  a  cavity  of  the  matrix  and  usually 
fills  this.  There  may  be  a  space  (lacuna)  due  to  shrinkage  of  the 
cell.  The  boundary  of  the  cavity  is  the  capsule;  this  resembles  the 
matrix  and  is  firmly  attached  to  it.  Sometimes  the  capsule  stains 
more  deeply  than  the  matrix.  The  capsule  is  a  product  of  secretion 
of  the  cell  and  represents  the  exoplasm.  It  is  cast  off,  as  a  rule, 
each  time  the  cell  divides.     Each  cell  may  be  individual  or  several 


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B  C 

Fig.  66. — Sections  of  Cartilage. 

A. — Hyalin  Cartilage,  a,  Fibrous  layer  of  perichondrium;  b,  genetic  layer 
of  perichondrium;  c,  youngest  chondroblasts;  d,  older  chondroblasts; 
e,    capsule;   /,    cells;    g,    lacuna.     B. — Elastic    Cartilage.     C. — White 

FlBROCARTILAGE. 

may  occupy  one  cavity.  This  is  due  to  the  fact  that  each  new  cell 
did  not  form  a  capsule  for  itself  after  division.  The  apposed  sides 
of  these  cells  are  flattened  by  pressure  of  one  against  the  other. 

The  intercellular  substance  varies.  In  the  hyalin  variety  it  is  ap- 
parently homogeneous;  white  fibrocartilage  is  composed  mainly  of 
white  fibrous  tissue;  in  yellow  fibrocartilage  it  is  composed  of  yellow 
elastic  fibers. 

Hyalin  Cartilage. — In  this  variety  the  cellular  elements  are  as 


CONNECTIVE    TISSUES 


119 


above.  They  are  quite  numerous  and  close  together  just  beneath 
the  perichondrium.  Farther  in  they  are  larger  and  more  widely 
separated  and  several  may  be  found  within  one  capsule. 

The  intercellular  substance,  or  matrix,  is  apparently  homogeneous. 
Upon  careful  study,  however,  and  often  without  treatment  with 
special  reagents,  it  shows  a  fibrillar  character;  in  this  fibrillar  mesh- 
work  is  seen  the  ground  substance,  which  is  homogeneous.  This 
fibrillar  structure  is  especially  noticeable  in  young  cartilages.  The 
ground  substance  is  formed  by  the  fusion  of  the  castoff  capsules 
and  usually  responds  to  mucin  stains. 


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Fig.  67. — A  Vertical  Section  of  Articular  Cartilage. 
a.  Bone;  b,  calcined  cartilage;  c,  perpendicular  groups;  d,  irregular  groups; 
e,  horizontal  groups,  parallel  to  the  surface.      (After  Schafer.) 

Articular  Cartilages. — In  these  the  cells  are  smaller  and  arranged 
in  short  rows.  At  the  perichondrium  the  rows  are  parallel  to  the 
surface  of  the  bone.  The  matrix  is  granular  and  after  maceration, 
under  pressure  it  separates  into  fibrils  that  run  vertical  to  the 
surface.     The  perichondrium  blends  with  the  periosteum. 

Hyalin  cartilage  is  found  covering  articular  surfaces  of  bones, 
as  the  costal,  nasal,  tracheal  and  most  of  the  laryngeal  cartilages. 


120  PRACTICAL   HISTOLOGY 

It  precedes,  with  a  few  exceptions,  all  the  bones  of  the  body,  and 
may  ossify  in  old  age. 

White  fibrocartilage  consists  of  islands  of  the  hyalin  variety, 
separated  by  an  intercellular  substance  made  up  of  delicate,  wavy 
bundles  of  white  fibrous  tissue  that  have  a  parallel  course.  The 
amount  of  hyalin  matrix  varies  in  these  cartilages.  In  the  inter- 
vertebral discs  the  cartilage  cells  are  more  numerous  toward  the 
central  pulp.  In  the  symphysial  cartilages  the  cells  are  more  numer- 
ous at  the  surface  attached  to  the  bone. 

This  variety  is  not  very  abundant  but  is  widely  scattered.  It 
is  found  as  marginal  cartilages  (deeping  joint  cavities) ;  as  the  inter- 
vertebral discs;  as  intra- articular  cartilages;  lining  grooves  in  bone 
where  tendons  move  and  occasionally  as  sessamoid  fibrocartilages 
in  tendons. 

Yellow  fibro-  or  elastic  cartilage  is  that  variety  in  which  the  inter- 
cellular substance  is  composed  of  elastic  fibers.  The  elastic  tissue 
forms  a  meshwork  in  which  the  hyalin  islands  are  found. 

It  is  practically  hyalin  cartilage  in  which  the  hyalin  matrix  has 
been  replaced  by  elastic  tissue.  The  cartilage  cells  are  found  in 
small  groups,  surrounded  by  only  a  small  amount  of  the  hyalin 
substance.  This  variety  never  ossifies  or  calcifies,  and  is  to  be 
looked  for  in  regions  where  elasticity  is  required,  as  in  the  epiglottis, 
ear,  Eustachian  (auditory)  tube  and  small  laryngeal  cartilages. 

Cartilage  contains  few  or  no  blood-vessels,  except  in  the  perichon- 
drium, and  during  the  developing  stage.  Lymph  channels  are  said 
to  be  absent,  so  that  its  nutrition  is  not  of  a  very  high  order. 

Upon  heating  cartilage  to  i2o°C.  in  a  hermetically  sealed  tube 
chondrin  is  obtained.  This  will  not  dissolve  in  either  alcohol  or 
cold  water.  It  is  precipitated  by  acetic  acid,  insoluble  in  an  excess 
of  this  but  soluble  in  some  mineral  acids. 

When  cartilage  begins  to  develop  the  polygonal  cells  of  the  mesen- 
chyme become  clearer  and  the  nucleus  more  distinct.  The  tissue 
immediately  surrounding  the  cells  also  becomes  clear  and  consti- 
tutes the  cohering  capsules  of  the  adjacent  cells  and  represents  the 
matrix.  If  the  matrix  remains  in  this  condition  permanently  it  is 
called  parenchymatous.  Glycogen  appears  early  in  the  cytoplasm 
of  these  cells.     This  is  followed  by  the  rapid  increase  in  size  and 


CONNECTIVE   TISSUES  121 

multiplication  of  the  cells  with  an  attendant  increase  in  the  matrix. 
As  the  cells  reproduce  the  old  capsules  are  cast  off  and  blend  with 
the  matrix  of  which  they  soon  become  an  indistinguishable  part.  In 
each  succeeding  division  more  cells  are  formed,  more  capsules  are 
cast  off  and  the  matrix  thus  becomes  increased  in  quantity.  As  a 
result  of  the  latter  condition  the  cells  come  more  widely  separated. 
According  to  Kolliker  the  capsule  is  secreted  by  the  cell,  but  accord- 
ing to  M.  Schultze  it  represents  the  superficial  cytoplasm  (exoplasm) 
of  the  cell. 

In  elastic  cartilage  the  matrix  is  at  first  entirely  hyalin.  Gradu- 
ally fine,  albumoid  granules  appear  in  the  matrix  close  to  the  cells 
and  gradually  extend  outward  toward  the  perichondrium.  From 
these  granules  the  elastic  fibers  are  derived.  The  fibers  of  the  white 
fibrocartilage  are  said  to  appear  at  the  same  time  as  the  matrix 
but  in  what  manner  is  not  exactly  known. 

Cartilage  regenerates.  When  a  cartilage  is  cut  the  wound  is 
healed  by  white  fibrous  tissue.  Later  this  is  gradually  transformed 
into  cartilage.  Costal  cartilages,  when  fractured,  heal  by  a  fibrous 
connection  often.  This  is  usually  very  dense  at  its  circumference 
and  ossification  may  later  occur  in  this  dense  tissue. 
.  o.  Bone  is  the  most  highly  differentiated  of  the  connective  tissues. 
It  is  characterized  by  the  presence  of  a  very  hard,  unyielding  inter- 
cellular substance  that  has  a  characteristic  arrangement. 

Bone  is  composed  of  inorganic  (66  per  cent.)  and  organic  salts 
(34  per  cent.);  the  former  are  soluble  in  mineral  acids,  by  which  they 
may  be  removed  and  the  tissue  cut.  The  latter  are  removed  by  burn- 
ing, after  wThich  process  the  inorganic  substance  remains  as  a  porous 
mold  of  the  bone.  The  earthy  material  gives  hardness  and  rigidity, 
while  the  animal  material  gives  tenacity  and  elasticity. 

Bones,  like  cartilage,  are  surrounded  by  a  fibrous  sheath,  the 
periosteum,  beneath  which  is  the  bone  substance  proper;  the  latter 
consists  of  cells  and  intercellular  substance. 

The  periosteum  of  young  bones  consists  of  three  layers,  fibrous, 
Hbroelastic  and  osteogenetic. 

The  fibrous  layer  is  composed  of  coarse  bundles  of  white  fibrous 
tissue  that  serve  to  connect  the  periosteum  to  the  surrounding  tissues. 


122 


PRACTICAL  HISTOLOGY 


The  fibroelastic   layer  consists  of  more  delicate  bundles  of  white 
fibrous  and  especially  elastic  tissues. 

The  inner,  or  genetic,  layer  is  rich  in  cells  and  capillaries  and  con- 
tains only  sufficient  white  fibrous  tissue  to  support  these.  These 
cells  are  the  future  osteoblasts  that  secrete  the  osseous  tissue.  From 
its  inner  surface,  it  sends  in  bundles  of  fibers  that  pierce  the  layers 
of  bone  at  right  angles,  and  bind  them  together.  These  are  Sharpens 
fibers.  Some  of  these  are  derived  from  the  tendons  inserted  into 
the  periosteum.     In  addition  there  are  the  lamellar  fibers.     These 

are  delicate  bundles  of  white  fibrous  con- 
nective tissue  that  pass  through  the  vari- 
ous lamellae  some  at  right  angles  and 
others  obliquely.  Some  of  the  fibers  are 
elastic.  In  the  adult,  after  growth  ceases, 
the  vessels  in  the  innermost  layer  of  the 
periosteum  are  reduced  in  number  and  the 
osteoblasts  are  only  sufficient  in  number 
for  the  purpose  of  regeneration  of  the 
bone.  The  fibroelastic  layer  becomes  cor- 
respondingly thicker. 

The  periosteum  not  only  gives  rise  to 
the  osteoblasts  but  also  serves  for  the 
support  of  blood-vessels,  nerves  and  lymph 
channels  and  for  the  attachment  of  muscles,  tendons  and  ligaments. 
The  cells  are  all  of  the  irregular  stellate  type,  and  consist  of  flat- 
tened bodies  and  short  processes  that  extend  into  small  canals,  to 
be  described  later.  The  cytoplasm  is  not  very  abundant,  and  the 
nuclei  are  oval,  and  often  vesicular.  No  doubt  but  that  the  osteo- 
blasts assist  in  the  nutrition  of  the  bone  by  modifying  the  nutritive 
elements  derived  from  the  blood  and  distributing  it  to  the  osseous 
tissue  through  the  lacunae  and  canaliculi.  These  latter  structures 
represent  the  cell  spaces  of  the  ordinary  connective  tissues.  The 
osteoblasts  are  homologous  to  the  lamellar  cells  of  areolar  tissue. 

The  intercellular  substance  is  hard  and  resistant  but  elastic.  It 
consists  of  osseous  material  that  is  secreted  by  the  cells,  and  is 
peculiarly  arranged  in  the  compact  variety.  It  contains  spaces,  or 
lacuncB,  from  which  extend  minute  canals,  or  canaliculi.     Beside 


Fig.  68. — A  Preparation 
of  the  Dura  Showing 
Sharpey's  Fibers,  the 
Hair-like  Projections 
on  the  Dura.  (Photo- 
graph.) 


CONNECTIVE   TISSUES 


123 


Fig.  69. — Lamella  Stripped  From  A  Decalcified  Parietal  Bone.     (Sharpey.) 

a,  a.  Lamellae    exhibiting   decussating   fibers  with  openings  for  the  perforating 

fibers,     b,  b,   Stripped  lamellae  with  the  perforating  fibers  c,  c. 


Fig.  70. — A  Section  of  Cancellous  Bone  Showing  the  Marrow  Reticulum 
and  Adipose  Tissue  between  the  Bony  Spicules.  (Photograph.  Obj. 
16  mm.,  oc.  S  X.) 


124 


PRACTICAL   HISTOLOGY 


these,  there  are  a  great  number  of  canals  that  vary  in  length  and 
diameter.     These  are  the  Haversian  canals. 

There  are  two  varieties — cancellous,  or  spongy,  and  compact, 
or  solid. 

Cancellous  bone  consists  of  spicules  and  lamellae  forming  a  network 
resembling  a  sponge,  or  lattice.  The  lamellae  run  in  the  direction 
of  the  greatest  strain.  The  spicules  have  a  lamellar  structure  and 
contain  delicate  Haversian  canals  surrounded  by  a  few  thin,  con- 
centric lamellae;  in  addition  there  are  little  spaces  called  lacunae. 
In  the  living,  or  recent  condition  these  spaces  are  occupied  by  osteo- 
blasts, the  bone-forming  cells. 


Fig.  71. — Cross-section  of  Human  Compact  Bone. 
a,  Periosteum;   b,    peripheral   lamellae;    c,    Haversian    canals;   d,    lacunae;  e, 
interstitial  lamellae;  /.  perimedullary  lamellae;  g,  marrow;  h,  Haversian  lamellae. 
(Stohr's  Histology.) 

This  variety  is  found  around  the  medullary  cavity  and  in  the 
extremities  of  the  long  bones,  and  forming  the  central  portion  of  the 
flat,  irregular  and  short  bones.  The  meshes  of  the  network  are 
covered  by  the  endosteum  and  are  filled  with  marrow. 

Compact  bone  has  a  characteristic  structure.  The  osseous  matter 
is  arranged  in  layers,  or  lamella,  between  which  lie  the  lacuna. 
There  are  four  varieties  of  lamellae:  (a)  periosteal,  peripheral, 
or  circumferential;  (b)  Haversian,  or  concentric;  (c)  intermediate, 
ground,  or  irregular;  and  (d)  perimedullary,  or  internal. 

(a)  The  peripheral,  periosteal,  or  external  lamellae  are  those  formed 


CONNECTIVE    TISSUES 


125 


directly  from  the  periosteum.  They  are  few  in  number,  and  several 
are  required  to  complete  the  circumference.  Between  them  are  a 
number  of  irregular  spaces,  lacuna,  from  which  little  canals  extend, 
the  canaliculi.  The  external  layer  has  a  number  of  small  depres- 
sions called  Hows/rip's  fovea  or  lacuna.  These  are  occupied  by 
large  bone-destroying  cells  called  osteoclasts.  Haversian  canals 
are  not  present,  but  larger  canals,  containing  blood-vessels  from  the 
periosteum,  are  seen.  These  are  Volkmamis  canals,  and  they 
communicate  with  the  Haversian  canals  farther  in. 


Fig.  72. — Cross-section  of  Compact  Bone  (Ground). 
a,  Haversian  canal;  b,  Haversian  lamellae;  c,  intermediate  lamellae, 
graph.     Obj.  16  mm.,  oc.  7.5  X.) 


(Photo- 


(b)  The  Haversian  lamellae,  which  are  probably  the  most  numerous, 
are  thin,  cylindric  layers  concentrically  arranged  around  a  small 
central  canal  called  the  Haversian  canal.  These  layers  are  separated 
in  places  by  the  lacunae,  and  pierced  by  the  canaliculi.  The  lamellae 
of  a  system  are  parallel  to  one  another,  but  the  different  systems 
usually  run  at  various  angles. 

An  Haversian  system  consists  of  the  lamellae,  canal,  lacunae  and 
canaliculi. 

The  Haversian  canals  are  occupied  by  blood-vessels,  nerves  and 


126 


PRACTICAL  HISTOLOGY 


lymphatics.  Those  nearest  the  marrow  cavity  are  the  largest, 
contain  marrow  and  communicate  with  the  marrow  cavity.  The 
short  canals  are  generally  parallel  to  the  long  axis  of  the  bone, 
anastomose  freely  with  one  another  and  measure  25^  to  125/u  in 
diameter. 

(c)  The  intermediate,  interstitial,  or  irregular  lamellae  lie  between 
the  Haversian  systems,  and  are  irregular  in  size  and  form.  They 
are  the  remains  of  Haversian  and  periosteal  lamellae,  altered  by  the 


<T    *      m  **■*    m-    ■"         *\; 


\  \  .-<• 


---,_- 


Fig.  73. — Longitudinal  Section  of  Compact  Bone  (Ground)  Showing 
Branching  Haversian  Canals.  The  irregular  dark  spots  are  the  lacunas. 
(Photograph.     Obj.  16  mm.,  oc.  7.5  X.) 


growth  of  the  bone  in  diameter.  No  canals  are  found  here,  but 
lacunae  and  canaliculi  are  present  between  the  lamellae. 

(d)  The  peri  medullary,  or  internal,  lamellae  are  not  very  regular, 
and    are   found    surrounding    the    medullary,    or    marrow    cavity. 

The  lacuna  are  small,  flat,  irregular  spaces  found  between  the 
various  lamellae  throughout  the  bone,  and  occupy  a  portion  of  each 
of  the  adjacent  lamellae,  and  do  not  lie  in  one  alone.  Each  space 
measures  from  13/i  to  31/x  in  length,  6ju  to  14/i  in  width  and  4/x  to 
9ju  in  depth.  The  walls  of  the  lacunae  and  canaliculi  are  more 
resistant  to  acids  than  the  remainder  of  the  osseous  tissue.     These 


CONNECTIVE   TISSUES  1 27 

spaces  are  said  to  be  lined  by  a  delicate  membrane  and  they  contain 
the  osteoblasts. 

Extending  in  all  directions,  are  small  canals,  or  canaliculi  (1 
to  2  microns  in  diameter),  that  communicate  with  those  of  other 
lacunae,  so  that  a  series  of  intercommunicating  spaces  results. 
Those  lacunae  lying  nearest  the  Haversian  canals,  communicate 
with  them,  but  the  peripheral  ones  of  a  system  do  not  communicate, 
to  any  great  extent,  with  those  of  the  interstitial  lacunae.  The 
canaliculi  serve  as  supports  for  the  processes  of  the  osteoblasts. 

The  compact  portions  of  the  extremities  of  bones  contain  no 
Haversian  systems  and  no  large  lacunae  so  that  pressure  can  more 
readily  be  borne.     Vessels  do  not  enter  the  bone  here. 

The  flat,  short  and  irregular  bones  consist  of  a  thin  shell  of  compact 
bone  covering  a  mass  of  cancellous  bone  that  constitutes  the  bulk 
of  these  bones.  Where  the  bones  are  thin,  or  have  small  processes, 
no  cancellous  bone  is  present. 

The  medullary  cavity,  which  contains  the  nutrient  marrow,  is  a 
large  space,  in  the  shafts  of  the  long  bones;  it  is  lined  by  the  endosteum 
which  is  analogous  in  structure  and  function  to  the  periosteum;  it 
also  constitutes  a  covering  for  the  marrow. 

The  marrow  is  of  two  varieties,  red  and  yellow.  The  red  marrow 
is  found  in  the  marrow  cavities  and  in  the  cancellous  bone  of  the 
extremities  of  the  long  bones  and  in  the  cancellous  tissue  of  the  flat 
and  irregular  bones,  in  young  persons;  in  adults  the  marrow  in  the 
marrow  cavities  becomes  yellow.  The  difference  is  due  to  the 
presence  of  a  great  deal  of  fat  in  the  yellow  marrow,  whereby  the 
color  becomes  changed.  It  is  not  a  blood-making  tissue  as  the 
cellular  elements  are  few  or  may  be  entirely  wanting.  In  disease, 
however,  it  may  again  become  red. 

The  red  marrow  consists  of  a  delicate  network  of  reticulum, 
derived  from  the  endosteum,  supporting  a  dense  capillary  plexus, 
nerves  and  lymphatics  and  a  number  of  different  cells.  These 
cells  are  (1)  myelocytes,  or  marrow  cells;  (2)  nucleated  red  blood  cells, 
or  erythroblasts;  (3)  erythrocytes;  (4)  white  blood  cells,  or  leukocytes; 
(5)  myeloplaxes;  (6)  osteoclasts;  (7)  osteoblasts;  (8)  fat.  The  red 
bone  marrow  is  the  most  important  red  cell-forming  tissue  in  the 
body  throughout  life. 


128 


PRACTICAL   HISTOLOGY 


i.  The  myelocytes  are  large  nucleated  masses  of  granular  cyto- 
plasm that  resemble  the  leukocytes  of  the  blood.  The  granules 
of  the  cytoplasm  are  in  some  of  these  cells  fine  and  neutrophilic 
or  acidophilic  in  reaction;  in  other  cells  they  are  coarse  and  baso- 
philic in  reaction.  The  nucleus  is  usually  large,  oval  and  lobulated 
and   the  chromatin  small  in  quantity.     Some  of   these  cells  are 


Neutrophile.     Lymphocytes.     Giant  cell. 


Eosinophile. 


Erythroblasts. 


Myelocytes. 


Erythrocyte. 


Neutrophile. 


C 


Premyelocytes. 

Mast  cell.  Erythroblast.  Border  of  a  fat  cell. 

Fig.  74. — Elements  of  Human  Bone  Marrow.     (Lewis  and  Stdhr.) 

A,  From  the  femur  at  10  years.     B,  from  a  cervical  vertebra  at  19  years.     C,  from 
•the  femur  at  77  years.     D,  from  a  rib  at  59  years. 

ameboid  and  phagocytic;  the  latter  contain  reddish-brown  pigment 
granules  that  are  probably  converted  hemoglobin.  Some  consider 
these  cells  as  derivatives  of  the  blood  lymphocytes  and  others 
maintain  that  they  are  the  ancestors  of  the  oxyphils  and  basophils 
of  the  blood. 

2.  The  erythroblasts  differ  from  the  erythrocytes  in  that  each 
contains  a  nucleus  and  this  may  show  mitotic  figures.     These  cells 


CONNECTIVE   TISSUES  1 29 

vary  somewhat  in  size  but  are  seldom  over  9.5/x  in  diameter.  By  the 
loss  of  the  nucleus  these  cells  become  the  erythrocytes,  or  normal 
red  blood  cells. 

Two  varieties  are  described:  The  erythroblasts  that  possess  a 
nucleus  rich  in  chromatin  network  and  poor  in  hemoglobin.  These 
cells  gradually  change  to  the  normoblasts  in  which  the  nucleus  shows 
no  chromatic  network  and  the  cytoplasm  is  rich  in  hemoglobin. 

Some  classify  all  of  the  nucleated  red  cells  as  erythrocytes  of  which 
the  megaloblast  is  the  original  cell,  the  normoblasts  and  erythroblasts 
modifications,  which  by  the  loss  of  the  nucleus  become  the  normal 
red  cells  or  erythroplastids  as  they  call  them. 

3.  Erythrocytes  (erythroplastids)  are  the  preceding  cells  that 
have  lost  their  nuclei  and  are  ready  to  enter  the  blood-stream.  The 
manner  in  which  the  nucleus  is  lost  is  still  questionable.  Some  state 
that  the  entire  or  fragmented  nucleus  is  extruded  (karyorrhexis); 
others  believe  that  the  nucleus  is  absorbed  (karyolysis);  Emmel 
has  found  that  the  red  cell  of  the  pig  is  formed  by  budding. 

4.  The  leukocytes  are  of  different  varieties  of  which  the  first  three 
varieties  below  given  are  the  most  numerous. 

(a)  The  finely  granular  oxyphil  [polymorphonuclear  neutrophil) 
is  7.5  to  ioai  in  diameter.  There  are  several  stages  of  these  cells, 
the  younger  showing  a  centrosome  and  nuclei  that  contain  only  a 
little  chromatin  and  fewer  modifications  of  shape  and  the  older  ones 
that  have  a  dense  chromatic  network  and  more  varieties  of  nuclear 
shapes.  The  younger  cells  are  said  to  be  capable  of  cell  division  to 
a  slight  extent  and  the  older  ones  not  at  all. 

(b)  Eosinophils  are  of  the  same  size  as  the  preceding.  They  differ 
from  these,  however,  as  the  granules  in  the  cytoplasm  are  much 
larger  in  size  but  fewer  in  number  and  strongly  acidophilic  in  reaction. 
The  younger  cells  contain  a  centrosome  and  are  capable  of  division 
but  the  older  ones  are  not. 

The  oxyphil  and  neutrophil  granules  are  probably  intracellular  in 
origin.  They  seem  to  arise  from  the  chromidia  extruded  from  the 
nucleus  and  so  are  originally  basophilic  in  reaction;  by  chemical 
changes  wTithin  the  cytoplasm  they  change  their  character.  Weiden- 
reich  believes  that  these  granules  represent  hemoglobin  from  the 


130 


PRACTICAL  HISTOLOGY 


disintegrating  red  cells  as  the  latter  are  numerous  in  the  marrow 
and  spleen. 

(c)  Basophils  (mast  cells)  are  believed  to  be  formed  in  the  red 
marrow.  The  nucleus  varies  in  shape  and  the  cytoplasm  contains 
a  number  of  large,  coarse,  basophilic  granules.  They  are  also  found 
in  areolar  tissue  where  they  probably  end  their  existence.  Some 
claim  that  these  cells  are  normally  found  in  the  blood-stream  but 
this  is  doubtful.  In  certain  diseases,  however,  they  increase  in 
number  in  the  marrow  and  spleen  and  are  also  found  in  the  blood 
under  those  conditions. 


Fig.  75. — Osteoclasts. 
A.  Ordinary  osteoclast.     B,  one  showing  a  striated  border.     C,  a  bone  trabecula 
from  the  mandible  of  a  calf  embryo  with  the  osteoblasts  at  the  ends  causing 
absorption  and  osteoblasts  covering  the  sides  and  depositing  bone.      {After 
Kolliker.) 

(d)  The  lymphocytes  are  the  smallest  of  the  leukocytes,  measuring 
from  5/x  to  7.5/i  in  diameter.  The  cytoplasm  is  small  in  quantity, 
does  not  stain  deeply  and  may  be  basophilic  in  reaction.  The 
nucleus  is  large  and  nearly  spherical  in  form  and  the  chromatin  stains 
readily.  These  cells  are  not  numerous  and  while  some  are  developed 
here  most  of  this  type  are  formed  in  the  lymphoid  structures  and 
organs. 


CONNECTIVE   TISSUES 


131 


(e)  The  hyalin  cells  {large  lymphocytes)  are  the  largest  leukocytes 
measuring  from  n/x  to  15/j  in  diameter.  They  are  said  to  be  derived 
from  the  lymphocytes  which  they  resemble.  The  nucleus,  however, 
does  not  respond  so  well  to  stains  so  that  the  whole  cell  has  an  hyalin 
appearance,  hence  the  name. 

A  more  detailed  description  of  these  leukocytes  will  be  found  under 
Blood. 

5.  Osteoclasts  are  very  large  spheroidal,  or  flattened  cells.  Their 
outline  is  regular  and  the  granular  cytoplasm  contains  two  to  ten  or 


Fig.  76. — Giant  Cell  of  Bone  Marrow  Showing  Multiple  Centrioles  at/. 

a,  b,  c,  d  represent  the  different  zones  of  cytoplasm;  e,  nucleus.     (Reference 

Handbook  of  the  Medical  Sciences.     After  M.  Heidenhain.) 


more  clear  round  nuclei.  These  cells  are  numerous  in  developing 
and  regenerating  bone.  The  side  of  the  cell  attached  to  the  bone 
is  often  striated.  They  are  also  found  in  connection  with  the  roots 
of  the  milk  teeth.  They  are  of  great  importance  in  bone  destruc- 
tion from  which  the  name  osteoclast  is  derived.  They  are  capable 
of  ameboid  movements  and  are  phagocytic. 

6.  Myeloplaxes,  or  megakaryocytes  are  also  giant  cells  30/i  to 
100 fj.  in  diameter.  The  cytoplasm  is  granular  and  the  large  single 
nucleus  is  usually  horseshoe-shaped  or  annular.     It  contains  a  large 


1,32  PRACTICAL   HISTOLOGY 

number  of  nucleoli  and  a  number  of  centrioles.  It  is  ameboid  but 
not  phagocytic.  The  blood  platelets  are  said  to  be  derived  from 
their  segmented  pseudopodia. 

7.  Osteoblasts  occur  at  the  periphery  of  the  marrow  along  the 
endosteum. 

8.  Adipose  tissue  is  seen  in  red  marrow.  During  adolescence  it 
gradually  increases  in  the  marrow  cavities  of  the  long  bones  and  so 
replaces  the  bulk  of  the  red  marrow,  forming  the  yellow  marrow. 
As  the  cellular  elements  in  this  are  very  few  it  is  no  longer  an  hema- 
topoietic structure. 

The  blood-vessels  of  bone  are  very  numerous.  In  the  flat, 
irregular  and  short  bones  many  vessels  penetrate  the  superficial 
compact  bone  and  enter  the  spongy  parts  branching  into  many 
channels  that  supply  the  marrow  and  osseous  tissue.  Another  set 
of  vessels  in  the  periosteum  supplies  the  supperficial  compact  bone 
and  the  underlying  spongy  bone.  In  the  long  bones  the  superficial 
portions  are  supplied  by  the  periosteal  vessels.  These  penetrate  the 
outer  compact  bone,  through  Volkmann's  canals,  and  branches  pass 
in  to  the  Haversian  canals.  At  the  extremities  these  periosteal 
vessels  send  branches  into  the  superficial  portion  of  the  spongy  bone 
also.  The  marrow  and  the  deeper  parts  of  the  bone  are  supplied  by 
what  is  commonly  called  the  nutrient  vessel.  This  is  usually  one 
large  trunk  that  enters  at  the  nutrient  canal  of  the  diaphysis, 
passes  to  the  marrow  and  forms  here  branches  that  proceed  toward 
each  extremity.  These  latter  branches  give  rise  to  vessels  that 
supply  the  marrow,  the  compact  bone  and  the  cancellous  bone. 
The  branches  of  the  two  systems  anastomose  freely.  The  veins 
start  in  wide  venous  capillaries  that  empty  into  large  venous  channels 
that,  in  cancellous  bone  run  in  bony  canals  separate  from  those  of 
the  arteries.  These  veins  are  thin-walled,  possess  no  media  and  are 
valveless.  They  issue  from  the  bones  through  numerous  large 
openings.  The  circulation  in  the  red  marrow  of  mammals  is  be- 
lieved to  be  an  open  one.  The  walls  of  the  venous  capillaries  are 
supposed  to  be  incomplete  permitting  the  passing  of  the  cellular  ele- 
ments of  the  marrow  into  the  blood-stream.  This  seems  doubtful 
for  in  this  case  there  would  be  nothing  to  prevent  the  abnormal  con- 
stituents, as  myelocyte,  myeloplaxes,  osteoclasts,  etc.,  from  entering 


CONNECTIVE    TISSUES  133 

the  blood-stream.     The  blood  coming  from  the  marrow  contains 
more  than  the  usual  number  of  leukocytes. 

Lymphatics  occur  in  the  periosteum  and  in  the  Haversian  canals 
in  which  they  may  entirely  surround  the  blood-vessels.  The  lymph 
passes  into  the  denser  parts  through  the  lacuna?  and  canaliculi. 

The  nerves  accompany  the  arteries  which  they  supply.  Whether 
or  not  any  come  into  relation  with  the  bone  cells  is  not  known.  In 
the  periosteum  nerves  supply  the  blood-vessels  and  also  sensor  organs, 
Pacinian  bodies,  are  found. 

Development  of  Bone. — Bone  is  not  a  primary,  but  a  secondary 
tissue.  It  is  preceded  by  cartilage  or  by  fibrous  tissue.  Bone 
developed  from  hyalin  cartilage  is  called  endochondral,  while  that 
developed  in  fibrous  tissue  is  referred  to  as  intramembranous  bone. 
The  area  where  bone-formation  begins  is  called  the  center  of 
ossification . 

Endochondral  bone  formation  is  the  process  by  which  the  hyalin 
cartilage  is  converted  into  spongy  bone.  It  is,  in  reality,  a  com- 
bined process,  for  so  soon  as  the  spongy  bone  is  formed,  this  is 
changed  to  the  compact  variety  by  the  intramembranous ,  or  periosteal 
method. 

When  ossification  begins,  the  cartilage  cells  in  that  vicinity 
begin  to  multiply  rapidly,  increasing  in  size  at  the  expense  of  the 
matrix,  which  shows  evidence  of  calcareous  deposits  above  and 
below  this  area;  the  other  cells  arrange  themselves  in  rows  parallel 
with  the  long  axis  of  the  bone.  This  grouping  of  the  cells  is  probably 
due  to  the  course  of  the  lymph  stream  and  the  pressure  exerted  by 
the  groups  upon  one  another.  Multiplication  is  most  rapid  in  the 
center  of  the  area,  and,  as  a  result,  the  new  cells  are  unable  to  form 
new  capsules  for  themselves;  in  consequence,  a  large  number  are 
seen  in  one  space  called  a  primary  areola,  or  marrow  space.  The 
cells  then  become  vesicular  and  shrunken,  do  not  respond  readily 
to  stains  and  show  signs  of  degeneration.  In  the  cartilage  be- 
tween these  spaces,  calcareous  material  is  deposited,  and  the  cells 
above  and  below  arrange  themselves  into  parallel  rows.  The  cells 
within  the  areolae  either  disappear  or  become  osteoblasts,  and  osteo- 
clasts (Stohr  and  others  believe  that  all  disappear).  The  latter, 
45  to  90  microns  long  and  30  to  40  microns  wide,  dissolve  the  carti- 


134  PRACTICAL  HISTOLOGY 

laginous  and  calcareous  partitions  between  the  spaces.  As  a  result 
of  the  latter,  larger  spaces  are  formed,  and  these  are  the  secondary 
areola.  The  osteoblasts,  lay  down  a  thin  layer  of  osseous  tissue 
upon  the  remaining  partitions,  so  that,  at  first,  these  consist  of  a 
core  of  calcific  material  covered  by  a  thin  veneer  of  true  bone. 
As  the  process  continues,  the  calcareous  matter  is  entirely  removed 
and  is  replaced  by  bone. 

While  these  changes  have  been  in  progress,  the  perichondrium 
has  become  the  periosteum,  which  now  forms  osteoblasts.  These, 
with  trabecular  of  the  periosteum  and  blood-vessels,  pass  inward 
toward  the  center  of  ossification,  and  enter  the  areolae.  This 
vascularization  forms  the  first  marrow.  The  blood-vessels  pass 
upward  and  downward  from  the  center,  following  the  process  of 
calcification.  Gradually,  the  delicate  rod  of  cartilage  is  converted 
into  a  rod  of  spongy  bone.  The  articular  portions  are  separated 
from  the  shaft  by  an  interposed  disc,  the  epiphyseal  cartilage. 

Periosteal  bone  formation  now  begins.  Upon  the  inner  surface 
of  the  periosteum  a  thin  layer  of  osseous  tissue  is  deposited,  and  the 
osteoblasts  remain  surrounded  by  a  small  space  that  is  continued 
along  its  processes.  This  space  and  its  continuations  are  the 
lacunce  and  canaliculi. 

With  the  formation  of  periosteal  bone,  the  various  lamella  are 
formed.  The  peripheral  are  deposited  beneath  the  periosteum. 
The  Haversian  system  and  lamella  are  formed  in  the  following 
manner.  From  the  inner  surface  of  the  periosteal  layer,  projections 
are  formed  at  various  angles.  These  meet  other  projections,  thereby 
enclosing  a  small  space,  the  primitive  Haversian  canal.  Osteoclasts 
gain  access  and  make  this  space  regular  and  larger.  Then  osteoblasts 
lay  down  layer  upon  layer  of  osseous  material  until  only  a  small 
channel,  the  Haversian  canal,  is  left.  The  remains  of  the  peripheral 
lamellae  between  the  various  systems  go  to  make  up  the  interstitial 
lamella. 

With  the  formation  of  the  peripheral  lamellae,  the  network  of 
spongy  bone  is  removed  from  the  center  by  osteoclasts.  This 
leads  to  the  formation  of  a  marrow  cavity.  As  the  bone  increases  in 
size,  the  cavity  increases  in  proportion,  by  the  destruction  of  the 
surrounding  bone.     During  the  prime  of  life,  bone  formation  exceeds 


CONNECTIVE   TISSUES 


135 


cavity  formation,  but  in  old  age,  the  reverse  is  the  case,  so  that  the 
shaft  becomes  thinner,  and  the  cavity  larger. 

Ossification   of    the   epiphyses   occurs   much   later.     The    blood 
vessels  from  the  diaphysis  invade  the  epiphysial  cartilage.     Ossi- 


b  c  d  e  f 

Fig.  77. — Cross-section  of  a   Developing  Bone  of  a  Human  Fetus  of 

Four  Months. 

a,  Periosteum;  &,  boundary  between  endochondral  and  periosteal  bone;  c, 
perichondral  bone;  d,  remains  of  area  of  calcification;  e,  endochondral 
bone;  /,/',  blood-vessel;  g,  g' ',  developing  Haversian  spaces;  h,  marrow; 
i,  blood-vessel  (Slohr's  Histology.) 

fication  begins  as  in  the  diaphysis  but  the  extremity  expands  by 
the  maintenance  of  a  layer  of  cartilage  around  the  periphery. 
The  cartilage  is  replaced  by  cancellous  bone  that  persists.  As 
long  as  the  bone  continues  to  grow  the  cartilage  layer  is  main- 


136  PRACTICAL   HISTOLOGY 

tained  and  is  permanent  upon  the  articular  surface.  Between 
each  epiphysis  and  the  diaphysis  a  pad  of  cartilage,  the  epiphysial 
cartilage,  is  maintained  until  full  growth  is  attained.  Then  ossifica- 
tion of  these  discs  unites  these  parts  completely.  Apophyses  are 
formed  in  the  same  manner. 

The   bone   increases  in   diameter   by   the   continued  addition   of 
peripheral  lamellae,  as  a  tree  grows  in  thickness.     It  grows  in  length 
by  the  interposition  of  a  disc  of  cartilage  between  the  shaft  and 
heads  of  the  bone.     The  perichondrium  of  this  disc  is  thicker  than 
the  periosteum  of  diaphysis  and  epiphysis  producing  thus  a  groove 
about  the  bone  at  the  site  of  the  disc.     This  is  the  ossification 
groove     In  this  disc,  new  cartilage  is  formed  by  its  perichondrium 
as  rapidly  as  ossification  occurs.     This  is  the  cambium  layer,  and 
should  it  ossify,  that  end  of  the  bone  would  no  longer  increase  in 
length.     This  change  occurs  normally  when  full  height  is  reached. 
In  man,  between  the  first  and  fifth  years,  the  long  bones  grow 
chiefly  in  length.     The  rate  of  growth  of  the  ends  of  a  bone  is 
not  the  same,  some  growing  more  rapidly  at  the  proximal  extremity 
and  others  at  the  distal  extremity.     As  the  bone  increases  in  length 
and  thickness  absorption  is  also  taking  place  as  pointed  out  above. 
This  is   carried  on  by   the  osteoclasts.     When  these  appear  and 
apply  themselves  to  the  bone  the  surface  with  which  they  are  in 
contact  seems  to  melt  away  and  a  lacuna  is  formed.     As  this  process 
continues  the  bone  gradually  disappears.     This  solvent  action  is 
probaby  due  to  a  secretion  from  the  osteoclast. 

This  method  of  bone  formation  occurs  in  all  bones  except  those 
of  the  face  and  of  the  vault  of  the  cranium. 

Intramembranous  bone  formation  is  the  process  whereby  osseous 
tissue  is  formed  within  white  fibrous  tissue  without  the  intervention 
of  cartilage.  At  the  center  of  ossification  the  mesodermal  cells 
become  enlarged,  increased  in  number  and  form  a  sort  of  a  membrane 
from  which  fibers  radiate  in  all  directions.  These  are  delicate 
collagenous  fibrils  called,  by  Sharpey,  osteogenetic  fibers.  Upon 
these  calcareous  material  and  later  osseous  tissue  are  deposited  by 
the  enclosed  mesenchymal  cells  that  have  become  osteoblasts. 
In  this  way  the  bony  spicules  of  the  developing  structure  are  formed. 
The  osteogenetic  fibers  spread  in  all  directions  and  almost  as  rapidly 


CONNECTIVE   TISSUES 


137 


are  covered  and  replaced  by  calcareous  material  and  osseous  tissues. 
As  these  spicules  anastomose  freely  with  one  another  spongy  bone  is 
produced.  Some  of  the  cells  form  an  inner  and  an  outer  layer  con- 
stituting the  periosteum  (i.e.,  skull  bones);  other  cells  become  much 
enlarged  and  secrete  osseous  tissue  and  are  the  osteoblasts.  The 
periosteums  now  form  periosteal  lamellae  as  in  the  shafts  of  long 
bones.  As  the  bone  increases  in  thickness  the  periosteal  lamellae 
in  the  center  are  removed  and  replaced  by  the  spongy  bone  or 
are  converted  into  this  by  the  action  of  the  osteoclasts. 


Fig.  78. — Section  of  the  Parietal  Bone  of  a  Fetus.  Development  of  intra- 
membranous  bone,  a,  a,  external  and  internal  layers  of  the  periosteum. 
(Photograph.     Obj.  16  mm.,  oc.  5  X.) 


As  the  bone  becomes  vascularized  the  mesenchymal  tissue  enclosed 
within  the  bony  meshes  constitutes  the  primitive  marrow.  This 
consists  of  marrow  cells,  osteoblasts  and  a  great  number  of  osteo- 
clasts. By  the  action  of  the  latter,  assisted  by  the  osteoblasts, 
the  internal  portion  of  the  bone  is  being  constantly  altered  during 
the  growth  period.  Upon  the  bony  spicules  the  mesenchyme  forms 
a  thin  membrane  upon  which  is  seen  a  layer  or  two  of  osteoblasts. 
This  is  the  primitive  endosteum. 

Such  bones  increase,  in  thickness,  as  above,  and  laterally  by 
the  maintenance  of  a  layer  of  fibrous  tissue  at  their  edges.     This 


138  PRACTICAL   HISTOLOGY 

is  the  cambium  layer  that  corresponds  to  the  epiphyseal  disc  of 
long  bones,  and  when  full  growth  is  attained,  this  layer  ossifies, 
and  union  occurs  between  the  various  bones. 

Bone  readily  regenerates,  providing  the  periosteum  is  present. 
In  fractures  the  fragments  are  united  by  an  excess  of  osseous  tissue 
called  callus.  This  may  be  preceded  by  the  formation  of  cartilage 
in  this  area.  Later  the  osteoclasts  model  the  sharper  portions  by 
absorption.  If  the  periosteum  be  removed  the  part  of  the  bone  be- 
neath this  area  dies.  If  a  part  of  the  bone  beneath  the  periosteum 
be  removed  and  the  periosteum  be  permitted  to  remain,  bone  will 
be  formed  beneath  it.  In  the  young  osteoblasts  of  the  marrow  are 
active  in  the  formation  of  callus. 

10.  Dentin  will  be  considered  under  the  teeth. 

n.  Blood  is  the  only  liquid  connective  tissue.  As  it  is  part  of  the 
circulatory  system,  it  will  be  considered  when  that  is  described. 


CHAPTER  V 
MUSCLE  TISSUES 

Muscle  tissue  is  a  special  tissue  that  produces  the  various  move- 
ments of  the  body  or  organs  whether  under  the  control  of  the  will 
or  not.  It  consists  chiefly  of  cellular  elements  in  the  form  of  fibers 
of  varying  shapes  and  lengths.  Intercellular  substance,  or  cement 
is  absent.  The  muscles  are  all  derived 
from  the  mesoderm  with  the  exception 
of  those  of  the  sweat  glands  and  iris. 
In  lower  animals  they  may  be  also  of 
ectodermal  and  entodermal  origin. 
Myoplasm,  as  yet  undifferentiated 
into  muscle  fibers,  is  contractile  as 
shown  in  the  developing  heart.  As 
the  primitive  muscle  cells,  or  myoblasts, 
are  formed  contractile  myofibrils  ap- 
pear in  them. 

Muscle  tissue  constitutes  the  flesh 
of  animals  and  is  classified  in  three 
varieties:  (i)  voluntary  striated,  or 
skeletal,  (2)  involuntary  nonstriated,  or 
smooth,  and  (3)  involuntary  striated,  or 
cardiac.  These  differ  markedly  in 
their  cellular  structure,  arrangement, 
distribution  and  function. 

Voluntary  striated  muscles  are  the 
most  highly  differentiated  of  the 
muscle  tissues  and  are  characterized  by  being  under  the  control 
of  the  will.  They  constitute  the  skeletal  muscles  and  even  some  of 
the  visceral  muscles.  Their  muscle  cells  are  arranged  in  masses 
called  muscles  which  are  usually  provided  with  a  tendon  at  each  end 
for  attachment  to  the  periosteum  of  the  bones. 

139 


Fig.  79. — Segment  of  a  Human 
Voluntary  Striated  Muscle 
Fiber  Showing  Dobie's 
Globules  (Intermediate 
Disc)  in  the  Light  Band. 
(Sharpey.) 


140 


PRACTICAL   HISTOLOGY 


Each  fiber,  or  cell  is  a  long  narrow  cylinder  and  its  cytoplasm 
constitutes  a  syncytium.  A  fiber  averages  about  i  inch  in 
length  though  in  the  Sartorius  muscle  they  may  reach  5  inches. 
The  diameter,  usually  25  to  80  microms  will  vary  in  the  same 
muscle.  The  largest  fibers  measure  about  100  microns  while  the 
smallest  are  about  10  microns  in  diameter.  In  the  male  the  fibers 
are  thicker  than  in  the  female  and  in  muscular  individuals  the 
diameter  is  greater  (in  the  same  muscle)  than  in  other  individuals. 


Q..<  f?"v 

2     h    <t 


Fig.  80.  Fig.  81. 

Fig.  80. — Segment  of  a  Longitudinal  Section  of  a  Voluntary  Striated 

Muscle  Fiber. 
h,   Hensen's  line  in  the  dark  band  Q;  z,  line  of  Dobie's  globules  in  the  light  band. 

(After  Bohm  and  Davidoff.) 

Fig.  81. — Segment  of   a  Voluntary   Striated    Muscle  Fiber   of   a  Crab 
undergoing  Fibrillation.     {After  Schdfer.) 

This  same  difference  in  thickness  in  different  muscle  is  not  apparent 
during  infancy.  Branched  fibers  are  found  occasionally  among  the 
muscles  of  the  human  tongue.  Such  fibers  are  numerous  in  the 
tongue  of  the  frog. 

Each  fiber  is  composed  of  a  large  number  of  fibrillce  imbedded  in  a 
substance  called  sarcoplasm.  These  fibrillar  are  surrounded  by  a 
delicate  tubular  sheath  called  the  sarcolemma.  This  is  composed 
of  a  tough,  homogeneous  substance  that  does  not  yield  when  the 
muscle  substance  ruptures.  This  sheath  is  more  prominent,  thicker 
and  stronger  in  lower  animals  (fishes,  amphibians)  than  in  mammals. 

The  fibers  show,  when  viewed  longitudinally,  light  and  dark  bands, 


MUSCLE   TISSUES  141 

or  lines  running  both  transversely  and  longitudinally.  The  longi- 
tudinal sir ia lions  are  due  to  the  alternation  of  the  dark  fibrillae 
and  the  lighter  sarcoplasm  in  which  they  are  imbedded.  Each 
fibril  or  sarco style,  consists  of  a  series  of  smaller  rod-like  parts.  These 
rods,  or  sarcous  elements,  are  separated  from  one  another  at  their 
ends  by  a  clear  space  filled  with  sarcoplasm  and  containing  a  small 
body  called  Dobie's  globule.  This  sarcoplasm  is  the  passive  sub- 
stance of  the  muscle  fiber  and  contains  the  glycogen.  Holmgren 
described  a  trophospongium  in  the  sarcoplasm  of  voluntary  striated 
muscle.  The  sarcous  elements  stain  darkly  and  are  doubly  re- 
fractile, or  anisotropic.  The  sarcoplasm  stains  palely,  is  semi-solid 
and  is  singly  refractile,  or  isotropic.  The  sarcoplasm  seems  anala- 
gous  to  the  hyaloplasm  of  the  ordinary  cells  and  serves  as  a  vehicle 

Transition  zone. 


\  \ 

Nucleus       tendon.  Q    Z 

Fig.  82. — Longitudinal  Section  of  a  Part  of  a  Muscle  Fiber  from  a  Human- 
Internal  Intercostal  Muscle,  Showing  its  Transition  to  Tendon. 
X750.     (Lewis  and  Stohr.) 

for  the  chemical  changes,  and  transference  of  nutrient  and  waste  mate- 
rials. The  fibrillae  correspond  to  the  spongioplasm  which  in  the 
muscle  cells  is  peculiarly  arranged  and  has  the  important  property  of 
powerful  contraction. 

The  cross-striations  consist  of  comparatively  broad,  uniform 
alternating  dark  and  light  bands  that  are  usually  more  distinct  than 
the  longitudinal  striations.  The  dark  band  is  doubly  refractile, 
or  anisotropic  and  the  light  band  is  singly  refractile,  or  isotropic. 

Each  band  averages  about  3  microns  in  breadth.  The  dark 
band  (Bruecker's  lines)  consists  of  a  row  of  sarcous  elements  (the 
rod-like  parts  of  the  sarcostyles)  extending  across  the  fiber  and  sepa- 
rated from  one  another  by  sarcoplasm,  so  that  each  dark  band  ex- 
hibits longitudinal  striations  which  are  continuous  with  those  of  the 


142 


PRACTICAL  HISTOLOGY 


other  bands.  Not  infrequently  the  middle  of  this  band  is  marked 
by  a  clear  transverse  line  called  the  disc  of  Hensen.  Upon  careful 
examination  each  light  band  is  seen  to  be  crossed 
at  its  middle  by  a  fine  and  usually  dotted  line. 
This  is  attached  peripherally  to  the  sarcolemma 
and  is  called  Dobie's  line,  or  the  membrane  of 
Krause.  The  parts  above  and  below  this  mem- 
brane are  referred  to  as  the  lateral  discs.  All 
parts  of  the  fiber  embraced  between  two  suc- 
cessive membranes  of  Krause  constitute  a  sar- 
comere. 

The  nuclei  of  a  voluntary  muscle  fiber  are 
very  numerous  (ioo  to  200).  Each  is  somewhat 
oval  in  shape  and  contains  a  network  of 
chromatin  and  one  or  two  nucleoli.  In  mam- 
mals the  nuclei  he  just  beneath  the  sarcolemma 
at  the  periphery  of  the  sarcous  substance.  In 
the  frog  they  are  imbedded  in  the  muscle  sub- 
stance. The  nuclei  are  more  numerous  at  the 
tendinous  ends  of  the  muscle  than  in  the  middle. 
\  The  sarcolemma  is  a  delicate  fibrous  sheath 
that  lies  close  to  the  fiber  substance.  It  is 
transparent,  homogeneous  and  tougher  and 
thicker  in  lower  vertebrates.  It  is  not  seen  as  a 
rule  except  in  special  preparations.  If  fresh 
muscle  tissue  be  treated  with  water,  the  muscle 
substance  ruptures,  and  the  delicate  membrane 
is  shown  spanning  the  interval. 

Upon  transverse  section  a  muscle  fiber  is  seen 
to  be  limited  by  the  sarcolemmal  sheath;  beneath 
this  are  seen  the  nuclei  located  at  the  periphery 
of  the  muscle  substance.     The  fibrillar  are  'seen 

oolemma.     (Jordan  .        .  .  11        1    "  1 

and  Ferguson,  after    to  be  arranged  in  the  form  of  small  polygonal 
Ranvier.)  areas  called  Cohnheim's  fields.     These  are  sepa- 

rated from  one  another  by  a  network  of  sarcoplasm.  This  network 
of  sarcoplasm  is  made  very  prominent  by  treating  the  muscle  tissue 
with  acid  and  gold  chlorid  after  the  method  of  Cohnheim. 


Fig.  83. — Ruptured 
Voluntary  Stri- 
ated Muscle 
Fibers  Showing 
the    Sarcolemma. 

a,  End  of  broken 
fiber;  m,  muscle 
fiber;  n,  nucleus;  p, 
shrunken  muscle 
substance;    s,    sar- 


MUSCLE   TISSUES 


143 


There  are  two  kinds  of  muscle  fibers,  red  and  white.  The  white 
fibers  predominate  in  man  and  are  poor  in  sarcoplasm  and  respond 
energetically  when  stimulated.  The  red  fibers  are  rich  in  sarcoplasm, 
are  usually  thinner  and  respond  more  slowly  to  stimulation.  These 
fibers  also  possess  more  nuclei  that  may  even  be  imbedded  in  the 
fiber.  In  the  rabbit  these  red  fibers  form  entire  muscles,  while  in 
man  they  are  scattered  among  the  white  fibers  in  the  Trapezius 
muscle. 


Fig.  84. — Section  of  Human  Voluntary  Striated  Muscle  Showing  Some 

Red  Muscle  Fibers. 

a.  a.  a,  Red  fibers  rich  in  sarcoplasm.     (Photograph.     Obj.  16  mm.,  oc.  7.5  X.) 


During  contraction  the  muscle  as  a  whole  becomes  shorter  and 
thicker.  The  changes  in  appearance  of  the  fiber  during  contraction 
have  been  studied  by  a  number  of  observers.  Merkel  believed  that 
the  muscle  substance  diffused  itself  over  the  entire  muscle  com- 
partment at  first  and  then  accumulated  at  the  membrane  of  Krause 
while  the  sarcoplasm  passed  to  Hensen's  discs,  the  substances,  thus, 
becoming  reversed.  According  to  Englemann  when  contraction 
begins  the  membranes  of  Krause  approach  one  another  and  the  parts 


144 


PRACTICAL   HISTOLOGY 


of  each  disc  become  indistinct,  the  striations  are  lost  and  the  discs 
appear  homogeneous.  As  the  contraction  progresses  the  striations 
reappear  and  the  light  disc  becomes  a  dark  band  compared  to  the 
clearer  disc  of  sarcous  substance.  In  reality  there  has  been 
no  change  of  position  of  the  discs,  as  Merkel  believed,  but  a  change  in 
refrangibility  accompanied  by  a  decrease  in  volume  of  the  dark  disc 
at  the  expense  of  the  sarcoplasm.  McDougal  advanced  the  theory 
that  the  shortening  of  the  sarcomeres  in  contraction  was  due  to  the 


Fig.  85. — Muscle    Showing   Lateral    Contraction*   "Wave.     (After   Rollet.) 


absorption  of  water  causing  the  sarcomeres  to  swell,  especially  in 
the  region  of  the  dark  discs.  He  later  stated  that  he  believed  the 
absorption  was  due  to  the  formation  of  lactic  acid  within  or  outside 
of  the  sarcomere.  The  contraction  must  be  due  to  the  movement 
within  the  sarcomere,  that  is  from  the  membrane  of  Krause  to  the 
sarcous  elements.  Englemann  later  believed  this  movement  to  be 
due  to  heat  developed  during  contraction  Another  view  is  the 
electrical  change  occurring  at  the  adjacent  surfaces  of  the  light  and 


MUSCLE   TISSUES 


145 


dark  portions  of  the  fibers  producing  a  change  of  surface  tension  at 

these  points.  MacDonald  believes  that  the  changes  in  the  muscle 
are  due  to  the  alteration  in  relation  of  the  protein  molecules  and  the 
electrolytes.  He  believes  that  the  onset  of  the  contraction  is  marked 
by  the  new  appearance  of  potassium  salts  in  the  central  portion  of 
each  sarcomere  producing,  thus,  a  difference  in  osmotic  pressure. 


Fig.  86. — Longitudinal  Section  of  Voluntary  Muscle  of  a  Guinea-pig, 
Injected,  Showing  the  Course  of  the  Capillaries,  a,  Ampullae. 
(Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 


A  muscle  consists  of  a  definite  collection  of  muscle  fibers.  The 
entire  muscle  is  enclosed  in  a  thin  sheath  of  white  fibrous  tissue  called 
the  epimysium;  this  sends  in  septa  that  divide  the  muscle  into  large 
secondary  bundles,  or  fasciculi.  The  secondary  bundles  are  composed 
of  a  number  of  primary  fasciculi,  each  of  which  is  surrounded  by  a 
sheath  called  the  perimysium.  From  the  perimysium  fibers  extend 
into  the  bundles  running  between  the  individual  muscle  fibers,  form- 
ing a  network  and  supporting  the  capillary  blood-vessels,  lymphatics 
and  nerves.  This  network  is  the  endomysium.  When  the  muscle 
10 


146 


PRACTICAL  HISTOLOGY 


fibers  form  the  tendon,  the  muscle  cells  end  abruptly  and  the  nuclei 
are  more  numerous  here.  The  tendon  bundles  begin  abruptly  and 
continue  parallel  to  one  another  while  the  areolar  tissues  of  the  mus- 
cle and  tendon  are  continuous. 

Muscles  are  very  vascular.  The  larger  vessels  pierce  the  epimy- 
sium  and  send  branches  along  the  septa  between  the  primary  bun- 
dles;   these   vessels   run  parallel  to  the  long  axis  of  the  muscle. 


&&TJ&P 


*^i*»   ^ri*    *^-^     -0^2/*^     *.' 


?£5- 


Fig.  87. — Trophocyte  in  Relation  with  a  Muscle  Fiber  of  the  Human 
Tongue.  The  nutritive  granules  are  being  "fed"  into  the  dark  discs. 
(TV anna  Svartz,  Anat,  Anz.,  March,  1914.) 


Branches  enter  the  primary  fasciculi  and  form  capillaries,  that  run 
parallel  to  the  long  axis  of  the  muscle,  forming  a  long  meshwork  be- 
tween the  fibers.  At  intervals  transverse  connections  between  the 
longitudinal  capillaries  are  seen  and  these  are  the  ampulla  that  serve 
to  take  the  tension  off  of  the  capillaries  during  muscle  contraction.  As 
a  rule  the  smaller  the  fibers  the  more  abundant  the  vessels  and  the 
closer  the  capillary  meshwork. 

The  nourishment  of  muscle  fibers  is  not  carried  on  in  the  usual  way. 
Holmgren  and  Timlin,  in  their  study  of  the  tissue  of  insects,  found 


MUSCLE   TISSUES  147 

special  cells,  tropliocytcs,  present;  these  took  from  the  blood  and  lymph 
the  various  nutritive  elements  and,  after  modifying  them,  trans- 
ferred the  products  to  the  tissue  cells.  These  trophocytes  are  neces- 
sary to  the  specialized  tissues  (muscle  and  nerve).  The  relation  of 
trophocytes  and  muscle  cells  has  more  recently  been  studied  by  Nana 
Svartz,  in  the  human  tongue.  The  trophocytes  are  large,  granular 
elements  that  clasp  the  muscle  cells.  The  granules  are  apparently 
nutritive  in  function  resembling  the  tigroid  bodies  of  the  nerve  cells. 
They  are  arranged  in  rows  and  are  passed  into  the  muscle  cells  and 
during  the  contraction  of  the  muscle  fiber  the  granules  dissolve. 
The  trophocytes  exhibit  peculiar  and  characteristic  changes  in 
appearance,  number  and  arrangement  of  granules  and  the  nucleus 
during  the  contraction  wave  of  the  fiber.  This  seems  to  indicate 
that  they  are  not  indifferent  cells.  The  direct  passage  of  substances 
from  the  trophoctyes  to  the  muscle  cells  is  demonstrable. 

Lymphatic  vessels  are  said  to  be  absent  in  voluntary  muscles. 
The  lymph  spaces  between  the  muscle  fibers  empty  the  lymph  into 
the  muscle  sheaths  and  tendon. 

The  nerves  are  large  and  enter  with  the  vessels.  They  pass 
between  the  fasciculi  and  anastomose  with  one  another.  After 
piercing  the  epimysium  the  nerve  follows  the  septa  to  the  primary 
fasciculi  and  separates  into  small  groups  of  fibers.  As  such  a  nerve 
does  not  contain  as  many  fibers  as  there  are  muscle  cells  each  nerve 
fiber  will  give  off  a  number  of  collaterals  or  branches  so  that  ulti- 
mately there  will  be  a  nerve  fiber  for  each  muscle  fiber,  and  one  pri- 
mary nerve  fiber  will  supply  a  number  of  muscle  fibers.  As  the  ter- 
minal nerve  fiber  pierces  the  sarcolemmal  sheath  the  neurilemma  and 
myelin  sheath  blend  with  the  sarcolemma  and  the  naked  axis  cylin- 
der alone  enters  the  muscle  substance.  This  passes  to  the  sole- 
plate  which  is  a  granular  mass  of  nucleated  protoplasm  containing 
several  nuclei.  Within  this  the  fibrillar  of  the  nerve  fiber  terminate 
in  bulbous  enlargements,  which, with  the  sole-plate  constitute  the 
end -plate.     There  is  but  one  organ  to  each  muscle  fiber. 

INVOLUNTARY  NONSTRIATED  MUSCLE 

The  involuntary  nonstriated,  or  smooth  muscle  tissue  is  less 
abundant   than   the  preceding   type  and  is  not  so  highly  differ- 


148 


PRACTICAL  HISTOLOGY 


K*;c  p 


Fig.  88. 

A. — Longitudinal  section  of  smooth  muscle  fibers:   a,  muscle  fiber;  b,  nucleus; 

c,  fibrous  tissue  between  fibers.  B. — Cross-section  of  smooth  muscle 
fibers:   a,  perimysial  connective  tissue;  b,  blood-vessel;  c,  nucleated  fiber; 

d,  nonnucleated  fiber.  C. — Longitudinal  section  of  voluntary  muscle 
fibers:  a,  sarcolemma;  b,  nucleus;  c,  end  of  muscle  fiber;  d,  dark  bands; 

e,  intermediate  disc;/,  nucleus;  g,  lateral  disc.  D. — Diagrammatic  section 
of  cross  and  long  striations:  a,  dark  disc;  b,  lateral  discs;  c,  intermediate 
disc.      E. — Cross-section    of    voluntary    muscle:    a,    perimysium;    b,    endo- 


MUSCLE    riSSUES  149 

entiated.  In  most  organs  the  fibers  are  arranged  into  distinct 
layers  and  not  in  the  form  of  muscles.  They  form  the  muscle 
coats  of  hollow  and  tube-like  organs.  The  fibers  are  said  to  be 
united  to  one  another  by  a  small  amount  of  intercellular  cement 
that  can  be  brought  out  by  the  silver  nitrate  method  of  staining. 
When  spaces  between  the  fibers  occur,  delicate  intercellular  bridges 
are  seen  connecting  the  cells  in  the  form  of  a  syncytium.  These 
bridges  are  the  continuation  of  the  peripheral  fibrillar  cytoplasm 
of  the  cells. 

Each  fiber,  or  cell  is  a  small,  spindle-shaped  element  measuring 
from  40  to  200  microns  in  length  and  3  to  8  microns  in  thickness. 
Larger  fibers  are  seen  in  the  pregnant  uterus  where  the  length  is 
often  500  to  600  microns  and  the  thickness  also  increased  in  pro- 
portion. In  the  aorta  and  some  of  the  larger  blood-vessels  these 
muscle  cells  are  very  irregular  in  shape.  The  ends  of  the  fibers 
may  be  branched  or  forked  as  in  the  aorta  and  bladder. 

The  sarcous  substance  may  show  longitudinal  striations  (but  no 
transverse)  due  to  the  presence  of  coarser  peripheral  fibrillar  and 
deeper  and  more  delicate  fibrils.  These  are  doubly  refractile  and  are 
separated  by  varying  amounts  of  sarcoplasm.  In  the  developing 
fibers  the  fibrils  arise  from  small  granules  that  are  apparently 
derived  from  the  mitochondria  and  are  called  myochondria.  The 
peripheral,  or  border  fibrils  are  coarser  and  are  the  ones  that  form 
the  intercellular  bridges;  they  serve  to  connect  the  cells  into  a 
syncytium.  The  deeper  are  the  more  delicate  and  seem  to  be  the 
ones  most  concerned  in  the  contraction  of  the  cells.  The  sarcoplasm 
may  contain  granules  at  the  poles  of  the  nuclei  and  immediately 
surrounding  the  nucleus  is  of  an  undifferentiated  character.  This 
contains  glycogen  granules,  lipoids  and  mitochondria. 

The  nucleus  is  usually  long  and  rod-shaped  and  located  in  the 
center  of  the  cell.  It  contains  a  distinct  chromatin  network  and 
one  or  two  nucleoli.     During  contraction  of  the  cell  the  nucleus 


mysium;  c,  nucleus  of  perimysium;  d,  fibrillae;  e,  nucleus  of  muscle;  /, 
sarcolemma.  F. — Longitudinal  section  of  cardiac  muscle  fibers:  a,  muscle 
fiber;  b,  nucleus;  c,  branch.  G. — Cross-section  of  cardiac  muscle  fibers: 
a,  perimysial  sheath;  b,  nucleus  of  sheath;  c,  muscle  fiber;  d,  nucleus;  e, 
radial  plates  of  fibrillae. 


150  PRACTICAL  HISTOLOGY 

becomes  shorter  and  thicker  (or  even  a  short  spiral)  and  the  chroma- 
tin seems  to  be  forced  towards  its  poles.  A  centriole  is  presentat 
the  side  of  the  nucleus. 

Although  a  sarcolemma  is  not  present  each  cell  is  surrounded 
by  a  delicate  membrane  which  may  be  a  layer  of  peripheral,  homo- 
geneous cytoplasm.  In  contracted  fibers  this  membrane  may  be 
wrinkled  giving  the  appearance  of  indistinct  transverse  striations. 

The  smooth  muscle  fibers  are  collected  into  fasciculi  of  varying 
sizes  that  are  usually  arranged  parallel  to  one  another  forming 
layers.  In  some  organs,  however,  these  fasciculi  interlace,  as  in 
the  uterus,  vagina  and  bladder. 

This  type  of  muscle  is  found  in  the  hollow  viscera  as  the  lower 
part  of  the  esophagus,  the  stomach  and  intestines,  the  trachea  and 
bronchial  tubes,  the  ureter,  bladder,  urethra,  penis,  the  ovaries, 
oviducts,  uterus  and  vagina,  the  ducts  of  glands,  the  skin,  the 
blood-vessels,  lymph  vessels,  the  eyeball  and  in  the  capsules  of 
certain  organs  as  the  spleen,  lymph  nodes  and  prostate. 

The  blood-vessels  are  less  numerous  than  in  the  voluntary 
striated  variety.     The  capillaries  form  plexuses  around  the  fibers. 

Some  organs,  as  the  stomach  and  intestines,  have  abundant 
lymphatic  plexuses  between  the  layers.  Other  organs  are  not  so 
well  supplied. 

The  nerves  are  from  the  sympathetic  system.  In  the  stomach 
and  intestines  these  amyelinated  nerves  form  a  prominent  plexus 
between  the  layers  of  the  muscle  coat  and  another  in  the  sub- 
mucous coat.  From  these  plexuses  the  terminal  fibers  pass  to  the 
muscle  fibers.  In  other  organs  there  may  be  more  delicate  plexuses 
or  simply  small  ganglia  in  relation  with  the  organs  and  from  these 
the  terminal  fibers  pass  to  the  muscle  fibers.  Here  the  nerve 
fibers  end  as  tapered  or  bulbous  extremities  that  are  applied  to 
the  surface  of  the  muscle  cells. 

INVOLUNTARY  STRIATED  OR  CARDIAC  MUSCLE 

The  cardiac  muscle  resembles  both  of  the  preceding  in  its  char- 
acteristics. The  fibers  are  cylindric  in  form  and  have  both  trans- 
verse and  longitudinal  striation,  as  in  the  voluntary  type.     Each 


MUSCLE   TISSUES 


151 


possesses  usually  a  single  nucleus,  which  is  centrally  placed,  and 
no  sarcolemma,  the  fibers  are  arranged  in  layers  and  are  not  under 
control  of  the  will  and  in  these  they  resemble  the  smooth  type. 

The  cardiac  muscle  fibers  are  usually  described  as  short  stubby 
cylinders  that  measure  100  to  200  microns  in  length  and  25  to  40 
microns  in  thickness.  These  branch  and  anastomose  freely  so  that 
there  is  a  continuity  of  the  fibers  through  both  sets  of  chambers 
of  the  heart.     As  a  result  of  this  anastomosis  and  the  continuity  of 


Fig.  89. — Section  of  Human  Cardiac  Muscle  Showing  Striations  and 
Branches.     (Photograph.     Obj.  4  mm.,  oc.  7.5  x.) 

fibrils  from  one  so-called  cell  to  another,  heart  muscle  constitutes 
a  syncytium.  The  cell  boundaries  are  not  clear,  but  for  the  sake  of 
description  the  term  cell  or  fiber  will  be  used.  Some  observers 
maintain  that  septa  do  occur,  indicating  transverse  segmentation, 
but  the  fibrils  are  seen  passing  through  these  septa  continuing  from 
one  cell  to  the  other. 

The  longitudinal  striations  are  due  to  the  presence  of  fibrillar  or 
sarcostyles,  imbedded  in  the  sarcoplasm.  Although  there  is  no 
distinction  between  deep  and  border  fibrils  as  in  the  smooth  type, 
still  the  fibrils  are  specially  arranged  in  rows  that  radiate  from  the 
central  area.     They  are  anisotropic.     These  fibrils  are  not  con- 


152  PRACTICAL   HISTOLOGY 

tinuous  but  interrupted  at  regular  intervals  so  that  as  in  voluntary 
striated  muscle  there  is  an  alternation  of  light  and  dark  bands  pro- 
ducing the  transverse  striatums.  The  light  bands  are  chiefly  sarco- 
plasm  containing  the  mitochondria,  glycogen,  liposomes,  lipoid 
and  albuminoid  granules.  This  band  is  divided  into  the  inter- 
mediate (Dobie's  membrane)  and  the  two  lateral  discs.  The  dark 
band  (Bruecker's)  is  crossed  by  the  line  of  Hen  sen. 

There  is  usually  a  single,  large,  oval  and  centrally  placed  nucleus, 
though  two  may  at  times  be  seen  in  one  cell.     The  chromatin  net- 


z 


eg 


Fig.  go. —  Muscle  Tissue  from  the  Adult  Heart  Showing  the  Interseg- 
mental Septa  and  the  Nuclei  Lying  in  the  Undifferentiated  Sarco- 
plasm.     (After  Palczewska.) 

work  is  distinct  and  each  nucleus  is  usually  surrounded  by  an  area 
of  undifferentiated  cytoplasm  containing  granules  and  fat  droplets. 
A  delicate  limiting  cell  membrane  is  present  and  some  call  it  a 
sarcolemma. 

The  muscle  fibers  of  the  atrioventricular  bundle  correspond  to 
the  Purkinje  fibers  of  the  hearts  of  lower  animals.  The  muscle 
fibers,  less  differentiated  than  those  of  the  myocardium,  are  striated 
but  the  sarcoplasm  predominates.  The  fibrillar  are  few  and  peri- 
pherally placed  forming  a  circle,  or  groups  that  are  irregular  or 
triangular.     The  volume  and  size  of  each  fiber  are  greater  than  in 


MUSCLE    TISSUES  153 

the  ordinary  cardiac  fibers.  They  are  less  branched  and  the  inter- 
calated discs  are  fewer  in  number.  The  cytoplasm  is  rich  in 
glycogen  and  pigment  granules  may  be  present.  Cell  boundaries 
cannot  be  definitely  located  so  that  this  tissue  is  a  syncytium.  This 
bundle  is  distinctly  separated  from  the  heart  muscle  and  seems 
to  appear  early  in  development.  It  has  to  do  with  the  conduction 
of  the  contraction  wave. 

According  to  some  investigators  the  heart  muscle  represents  a 
syncytium  in  which  no  distinct  cell  boundaries  are  to  be  detected. 
Others  maintain  that  their  individual  cells  as  above  described  are 
shown  by  special  stain  methods.  After  treatment  with  special 
reagents,  the  muscle  syncytium  seems  to  be  separated  at  fairly 
regular  intervals  by  the  inter collated  discs;  these  may  be  straight 
bands,  step-like  or  serrated.  These  are  irregular  as  to  form  and 
position.  These  may  extend  across  the  fiber  or  only  a  short  dis- 
tance. They  may  be  arranged  annularly  or  in  spiral  form.  They 
are  merely  peripheral  in  position  never  extending  all  of  the  way 
through  a  fiber  or  even  in  to  the  axial  core  of  sarcoplasm.  They  are 
permanent  structures  and  are  composed  of  units  corresponding 
to  portions  of  a  single  fibril  that  may  be  granular  or  compact.  They 
appear  late  in  fetal  life.  Some  believe  them  to  be  due  to  a  "  fixed 
phase  of  contraction  wave"  or  due  to  an  irresistible  strain  con- 
dition. The  fibrillae  continue  through  the  discs  from  one  so-called 
cell  to  another. 

The  blood-vessels  are  very  numerous  in  the  heart.  The  capil- 
laries lie  in  close  relation  with  the  muscle  substance  and  may  even 
lie  in  grooves  on  the  fibers.  In  some  animals  the  capillaries  are 
seen  imbedded  in  the  muscle  substance. 

The  lymphatics  are  very  numerous  and  follow  the  course  of  the 
blood-vessels.  The  lymph  capillaries  form  a  network  throughout 
the  intermuscular  tissue  forming  vessels  that  pass  toward  the 
serous  surfaces  and  ultimately  toward  the  base  of  the  heart. 

Cardiac  muscle  is  supplied  by  the  sympathetic  nerve  system.  These 
fibers  may  form  delicate  plexuses  at  the  intersections  of  which  are 
found  ganglia  of  various  sizes.  Individual  amyelinated  fibers 
extend  to  each  muscle  cell  and  terminate  upon  its  surface  in  one  or 
more  granules  or  bulbs.     According  to  Huber  and  others  the  nerve 


154  PRACTICAL   HISTOLOGY 

fibers  terminate  in  many  fine  fibrils  that  spread  over  each  nucleated 
segment  or  cell. 

Muscle  tissues  are  derived  from  special  portions  of  the  mesoderm 
called  myotomes,  or  muscle  plates.  The  cells  that  form  the  muscle 
fibers  are  the  myoblasts  and  they  multiply  very  rapidly.  In  the 
formation  of  the  voluntary  striated  muscles,  the  myoblasts  elongate 
and  increase  in  number.  The  myoblasts  become  separated  from  the 
mesenchymal  cells,  the  latter  forming  the  fascia  and  tendons.  The 
protoplasm  contains  granules  that  are  the  mitochondria,  according 
to  Meves  and  Duesburg.  The  fibrils  develop  independently 
of  one  another.  During  the  second  month,  in  the  human  embryo, 
the  granules  form  peripheral  longitudinal  striae  (the  future  muscle 
substance)  and  a  delicate  membrane  appears  derived  probably 
from  the  mesenchvme.  The  nucleus  lies  in  the  central,  undifferen- 
tiated cytoplasm.  More  striae  are  formed  and  by  the  regular  in- 
terruption of  the  fibrillae  the  cross  striations  appear.  By  the  sixth 
month  of  fetal  life  there  remains  but  a  small  central  core  of  un- 
differentiated cytoplasm  containing  the  nucleus.  Later  the  nuclei 
multiply  and  assume  a  peripheral  location.  In  the  trout  embryo 
the  first  fibril,  by  a  radial  longitudinal  splitting,  forms  a  peripheral 
ring  of  fibrils  and  the  central  fibrils  are  formed  by  a  splitting  of 
those  of  the  peripheral  ring.  As  the  central  area  becomes  invaded 
by  the  fibrils  the  nuclei  migrate  to  the  periphery  or  occupy  the 
deeper  portion  according  to  the  cell.  The  remaining  undifferen- 
tiated cytoplasm  between  the  fibrils  constitutes  the  sarcoplasm. 
Thus  the  white  fibers  are  formed.  In  the  red  fibers  fewer  fibrils 
are  formed  and  the  sarcoplasm  predominates.  This  variety  repre- 
sents an  intermediate  form  between  the  myoblasts  and  the  white 
variety. 

Most  of  the  smooth  muscles  are  derived  from  the  myoblasts  of 
the  mesoderm;  the  exceptions  are  the  muscles  of  the  sweat  glands 
and  the  iris,  which  are  of  epithelial  origin.  In  either  case  the  cells 
elongate  and  become  spindle-shaped  while  the  nucleus  elongates. 
The  cytoplasm  gradually  shows  the  formation  of  fibrils  that  soon 
completely  occupy  the  cytoplasm.  These  fibrils  become  differ- 
entiated into  central  finer  and  peripheral  coarser  ones;  the  latter 
are  supposed  to  arise  by  the  fusion  of  the  finer  ones  and  continue 


MUSCLE   TISSUES 


155 


from  one  cell  to  another.  These  fibrils  are  continuous  and  un- 
interrupted so  that  transverse  striations  do  not  appear. 

The  early  stages  of  the  cardiac  muscle  are  similar  to  the  above. 
Later,  however,  the  cells  seem  to  join  to  form  a  syncytium. 

After  becoming  completely  developed  voluntary  striated  fibers 
continue  to  increase  in  size  to  birth  and  from  that  time  to  adult 
life.  They  double  their  size  in  the  last  half  of  gestation  and  in  the 
adult  are  about  five  times  the  size  as  at  birth.  The  increase  in 
the  number  of  muscle  cells  is  due  to  the  presence  of  myoblasts  in 
the  muscles,  even  in  the  adult. 

Although  formerly  it  was  believed  that  muscle  tissue  did  not 
regenerate,  it  appears  that  diseased  or  cut  areas  are  later  joined 
by  muscle  tissue.  Some  consider  this  due  to  the  presence  of  myo- 
blasts but  Schmincke  states  that  the  existing  fibers  bud  at  the  ends. 
Pfitzner  found  that  in  artificially  produced  lesions  of  smooth  muscle 
tissue  regeneration  occurs  by  the  neighboring  cells  multiplying 
by  karyokinesis. 

The  accompanying  table  gives  a  resume  of  the  general  character- 
istics of  the  various  types  of  muscle  tissue. 


Characteristic 

Voluntary  striated 

Smooth 

Cardiac 

Shape. 

Long  cylinder. 

Spindle. 

Stubby  cylinder.  (?) 

Length. 

1-5  inches. 

25-500 

100-200  microns. 

Nucleus. 

microns. 

Number. 

Many. 

One. 

One. 

Location. 

Peripheral. 

Central. 

Central. 

Shape. 

Intermediate. 

Rod. 

Oval. 

Striations. 

Cross  and  long. 

(Longitudinal) 

Cross  and  long. 

Sarcolemma. 

Present. 

None. 

None. 

Branches. 

Occasional. 

(Occasional.) 

Always. 

Arrangement. 

In  masses  called 

In  layers. 

As  a  syncytium. 

i 

muscles. 

Control. 

By  will. 

Not  by  will. 

Not  by  will. 

CHAPTER  VI 
NERVE  TISSUES 

The  nerve  tissues  are  the  most  highly  differentiated  of  all  of  the 
tissues.  By  means  of  these  the  various  organs  and  structures  are 
connected  and  associated  so  that  they  can  work  together  and  accom- 
plish some  definite  object.  By  means  of  the  nerve  system  the 
individual  is  made  cognizant  of  his  environments  through  his  sense 
organs.  Nerve  tissues  consist  of  cells  and  intercellular  substance 
like  the  other  varieties  of  tissues  and,  as  in  connective  tissues,  the 
intercellular  substance  predominates. 

There  are  two  varieties,  gray  and  white.  The  gray  is  characterized 
by  a  grayish  color:  in  the  cerebrum  and  cerebellum  it  is  divided  into 
layers  while  in  the  spinal  cord,  brain  stem,  and  ganglia  the  arrange- 
ments is  somewhat  different.  It  consists  of  cells  and  their  processes, 
myelinated  and  amyelinated  nerve  fibers  and  neuroglia,  the  special 
supportive  substance  of  the  nerve  system.  The  white  nerve  tissue 
of  the  central  nerve  system  consists  chiefly  of  myelinated  nerve  fibers 
and  neuroglia  and  a  small  amount  of  white  fibrous  connective  tissue. 
The  peripheral  nerve  system  consists  of  nerve  fibers  supported 
mainly  by  white  fibrous  connective  tissue,  and  some  ganglia. 

The  nerve  system  consists  of  a  series  interrelated  and  intercon- 
nected units  that  give  a  continuity  of  impulse  from  the  central 
system  to  the  periphery  and  vice  versa.  These  units  are  called  the 
neurons;  each  neuron  consists  of  the  nerve  cell  and  its  various 
processes.  The  nerve  cell  comprises  the  cyiom,  or  cell  body,  the 
immediate  dendritic  processes  and  the  proximal  portion  of  the  axone. 
The  distal  portion  of  the  axone  and  the  distal  portion  of  the  main 
dendrite,  if  it  leaves  the  gray  substance  and  becomes  a  nerve  fiber  as 
in  the  sensor  system,  constitute  the  nerve  fibers.  These  fibers  may 
be  but  a  few  millimeters  in  length  or  several  feet,  as  evidenced  by 
those  nerves  of  the  extremities. 

156 


NERVE   TISSUES 


157 


Nerve  cells  are  found  only  in  gray  nerve  tissue.  A  typic  nerve 
cell  consists  of  a  cell  body,  from  which  a  number  of  processes  extend, 
a  nucleus,  nucleolus  and  centrosome.  The  whole  structure  com- 
prises the  neuron,  or  neurocyte. 


Fig.  91. — Typic  Nerve  Cells. 
a.  From  a  human  spinal  cord;  b.  from  the  motor  area  of  the  human  brain  showing 
tigroid  bodies.     Drawn  from  slides.      (Radasch,  Reference  Handbook  of  the 
Medical  Sciences.) 

The  cell-body,  or  cytom  is  composed  of  a  granular  and  fibrillar 
cytoplasm;  the  latter  at  the  point  of  origin  of  the  main  process 
forms  the  axis  cylinder  hillock.  The  fibrillar  network  is  of  two  kinds. 
A  fine  meshwork,  seemingly  containing  myelin,  was  found  by  Golgi. 


i*8 


PRACTICAL   HISTOLOGY 


It  stains  darkly  after  prolonged  exposure  to  osmic  acid  and  is  un- 
connected with  the  neurofibrils.  The  others  are  the  neurofibrils 
that  can  be  seen  only  after  careful  preparation  after  Golgi's  method 
and  must  be  examined  under  a  high-power  objective. 

Neurofibrils)  first  described  by  Max  Schultze,  are  seen  passing 
into  and  through  nerve  cells  without  forming  junctions  with  one 
another  and  extend  also  into  all  of  the  processes.     These  fibrils  are 


Fig.  92. — Nerve  Cells  Showing  Neurofibrils. 
A,  From  the  anterior  corpora  quadrigemina  of  a  kitten.     B,  From  a  spinal 
ganglion  of  an  embryo.      (After  Cajal.) 

of  a  semi-solid  nature,  apparently,  as  they  easily  become  varicose 
in  form;  they  vary,  apparently,  with  functional  activity.  Cajal  and 
Tello  have  found  that  in  the  hibernating  lizard,  during  winter  sleep, 
these  fibrils  are  less  numerous  and  thicker  than  in  the  active  animals. 
These  fibers  pass  from  one  cell  to  another  and  terminate  there. 
These  fibrils  respond  readily  to  the  intravitam  methylene  blue  and 
silver  nitrate  stains. 

In  the  meshes  of  the  fibrils  are  seen  the  granules  and  a  homo- 
geneous substance  that  stains  but  faintly.  The  latter  is  comparable 
to  the  hyaloplasm  of  the  typic  cell.  The  granules  are  of  two  kinds, 
oxyphilic  and  basophilic.  The  oxyphilic  granules  are  the  more  numer- 
ous and  the  smaller  and  are  seen  only  after  special  stains  have  been 


NERVE    TISSUES 


159 


employed.     The  basophilic  granules,  or  corpuscles  of  Nissl,  are  large 
but  inconstant. 

The  corpuscles  of  Nissl,  or  tigroid  bodies  consist  of  nucleoprotein 
containing  organically  combined  iron,  as  pointed  out  by  MacCallum. 
The  tigroid  nuclein  is  soluble  in  weak  solutions  of  soda.  They  are 
usually  large,  flake-like  bodies  that  respond  readily  to  methylene 
blue,  thionin,  or  toluidin  blue  stains.  They  are  derived  from  the 
nucleus  appearing  first  in  the  form  of  chromidia.     The  presence  and 


Fig.  93. — Motor  Nerve  Cells  from  the  Brain  of  a  Dog. 
a.  Normal   resting   cell;  b.  fatigued   cell.     (Schafer  after  Mann.) 


position  of  these  bodies  depends  upon  the  functional  activity  of  the 
cell;  they  may  be  scattered  or  arranged  in  two  groups,  one  near  the 
nucleus  and  one  near  the  periphery  of  the  cell;  they  may  be  arranged 
concentrically  around  a  well  defined  centrosome.  In  fatigued  cells 
they  disintegrate  and  disappear  although  Dollay  has  shown  that 
if  the  activity  is  not  excessive  they  first  increase  in  amount.  These 
changes  are  called  chromatolysis,  or  Nissl' s  degeneration.  Similar 
changes  occur  in  these  granules,  if  the  axones  of  the  cells  be  cut, 


160  PRACTICAL  HISTOLOGY 

twenty-four  to  forty-eight  hours  after  section  and  being  completed 
in  fifteen  to  twenty-four  days.  Various  poisons  including  toxins 
produce  a  like  effect.  With  removal  of  the  cause  regeneration 
usually  takes  place.  In  disease,  or  section  of  the  axone  regeneration 
does  not  take  place.  Crile  believes  that  Nissl's  substance  is 
volatile  and  unstable  and  depends  upon  adrenalin  for  its  existence. 
The  tyroid  bodies  are  seemingly  nutritive  in  function. 

In  certain  portions  of  the  nerve  system  other  granules,  usually 
brownish-yellow,  or  black,  are  found  in  the  cytoplasm.     This  is  the 

substantia  nigra  of  the  locus  cceruleus. 
This  pigment  contains  lecithin  and 
tends  to  increase  with  age,  making  its 
appearance  at  about  the  third  year. 
It  is  more  common  in  man  than  in  the 
lower  animals. 

Schirkogoroff  studied  themitochondria 

in   the   nerve   cells   of  the    rabbit  and 

found    them    more    or   less   abundant. 

They  were  best  developed  in  the  cells 

Fig.  9  4.-Trophospongium     of     the        inal    cord     oblongata    and 

within  a  Ganglion  Cell.  .    .      r  7  ° 

(After  Holmgren.)  Purkinje  cells  of  the  cerebellum,  in  the 

small  cells  of  the  basal  ganglia  of  the  brain 
they  were  small  and  few  in  number.  Their  presence  in  the  axones 
is  doubtful  though  some  state  that  they  are  found  in  all  of  the  cell 
processes.  They  have  also  been  found  in  the  spinal  ganglion  cells  of 
man  and  are  probably  concerned  with  the  metabolism  of  the  cell. 

Holmgren  has  found  a  fine  network  of  juice  canals,  or  tropho- 
spongium,  in  the  cytoplasm  of  many  of  the  nerve  cells,  especially 
those  of  the  ganglia.  He  believes  that  these  canals  may  undergo 
constant  changes. 

Golgi  and  others  have  described  a  reticular  investment  covering 
the  nerve  cell  and  extending  for  a  variable  distance  upon  the  proc- 
esses. Its  nature  and  function  are  unknown.  Some  believe  that 
it  represents  an  interlacement  of  the  terminal  ramifications  of  the 
axones  of  other  cells;  others  believe  that  it  is  of  neuroglial  origin. 
Around  nerve  cells,  especially  of  the  ganglia,  there  is  a  well  defined 
lymph  space  that  is  lined  with  endothelial  cells. 


/«► 


NERVE   TISSUES  l6l 

The  nucleus  is  usually  large,  pale  and  eccentrically  placed.  The 
nuclear  membrane  is  distinct  and  stains  deeply.  The  chromatin 
is  scant,  the  karyosomes  few  and  small  and  usually  attached  to  the 
inner  surface  of  the  nuclear  membrane.  At  times  chromatophilic 
granules  are  found  in  the  nucleoplasm. 

The  nucleolus  is  usually  very  large  and  stains  deeply.  It  is 
located  near  the  middle  of  the  nucleus  and  is  usually  readily  dis- 
cernible with  the  low  power. 

Centro somes  with  attraction  spheres  have  been  found  in  the  nerve 
cells  of  some  mammals. 

Cell  Processes. — Extending  from  the  cytom  will  be  found  one  or 
more  processes  and  cells  are  classified  according  to  their  number_as 
unipolar,  bipolar  and  multipolar.  The  main  process  is  called  the 
axone  and  the  other  the  dendrite. 

The  main  process  is  called  the  axone,  axis  cylinder,  or  neurit  and 
represents  a  direct  continuation  of  the  cytoplasm  of  the  cytom.  It 
starts  at  the  axis  cylinder  hillock  and  consists  of  a  cylindric  collection 
of  neurofibrils  imbedded  in  neuroplasm  and  surrounded  by  a  delicate 
membrane  called  the  axilemma.  The  presence  of  this  membrane  is 
denied  by  some.  The  axis-cylinder  hillock  and  the  process  are  devoid 
of  granules.  The  process  is  uniform  in  diameter,  smooth  in  contour 
and  may  give  off  branches  called  collaterals;  these  are  said  to  be 
more  numerous  near  the  proximal  than  the  distal  end  of  the  axone. 
Near  its  termination  the  axone  may  bifurcate.  Both  axone  and 
collaterals  usually  end  in  a  brush-like  mass  of  branchlets  called 
telodendria  (better  teleneurites).  At  times  these  terminals  are 
knobs  or  plates.  Occasionally  an  axone  may  arise  from  a  den- 
drite. The  axone  extends  a  variable  distance  from  the  cytom 
and  its  course  as  to  whether  it  remains  in  the  gray  substance  or 
leaves  it  gives  rise  to  a  classification  of  nerve  cells  into  first  and 
second  types. 

A  cell  of  the  first  type  (Deiter's  cell)  is  one  in  which  the  axone 

leaves  the  gray  substance  to  become  a  myelinated  nerve  fiber,  or  a 

sympathetic  nerve  fiber.     A  cell  of  the  second  type  (Golgi's  cell) 

is  one  in  which  the  axone  does  not  leave  the  gray  substance.     Tn  a 

unipolar  cell  the  single  process  soon  divides  into  two,  one  the  axone 

and  the  other  the  dendrite. 
11 


l62 


PRACTICAL  HISTOLOGY 


Fig.  95. 
Multipolar  cell  from  cerebral  cortex.  B.  Multipolar  cell  from  spinal  cord. 
C.  Pyramidal  cell  from  cerebral  cortex.  D.  Unipolar  cell.  E.  Bipolar  cell. 
F.  Cell  of  Purkinje,  antler  cell.  G.  Mossy  cell.  H.  Spider  cell.  I.  Cell  from 
spinal  cord  of  an  ox,  showing  pigment  granules.  K.  Ganglion.  L.  Sympathetic 
or  amyelinated  fibers.  M.  Longitudinal  section  of  myelinated  nerve  fiber: 
a,  neurilemma;  b,  myelin  sheath;  c,  axis  cylinder;  d,  node  of  Ranvier;  e, 
nucleus.  N.  Cross-section  of  osmicated  nerve  fibers.  O.  Myelinated  nerve 
fiber  of  a  guinea-pig  showing  the  reticulum.  P.  Myelinated  nerve  fibers  of  a 
toad,  showing  reticulum  (neurokeratin).  R.  Motor  neuron,  showing  nerve 
cell,  dendrites,  axis  cylinder  and  ending  of  latter  in  a  muscle.  S.  Cross-section 
of  nerve  trunk. 


NERVE   TISSUES 


163 


The  dendrites,  or  dendrons  are  secondary  processes.  As  they 
arise  from  the  cytom  they  are  relative  thick,  but  as  they  branch 
repeatedly  they  taper  rapidly.  These  branches  do  not  usually 
extend  far  from  the  cell-body  and  terminate  in  fine  branches, 
telodendria,  that  end  in  relation  with  the  telodendria,  or  teleneurites 
of  neighboring  cells.  Occasionally  the  dendrite  does  not  branch 
until  it  is  quite  a  distance  from  the  cytom;  this  is  the  case  in  the 
sensor  cells  in  the  various  ganglia  connected  with  the  sensor  nerves, 
where  the  dendrites  will  be  several  feet  in  length  and  reach  the 
periphery  before   they  arborize.     The  network  produced  by  the 


Fig.  96. — Cells  from   Cerebrospinal    Ganglia   Showing   Intracapsular 
Knobbed  Dendrites  c,  c;  a,  a,  Axones.     {After  Cajal.) 

various  telodendrites  forms  a  considerable  portion  of  the  gray  nerve 
tissue.  The  thorny  appearance  of  dendrites  in  Golgi  preparations 
is  due  to  the  presence  of  minute  lateral  projections  called  gemtnules. 
Unipolar  cells  possessing  but  one  process,  are  found  in  the  ganglia 
of  the  dorsal  roots  of  the  spinal  nerves  and  in  the  ganglia  connected 
with  the  trigeminal  and  vagal  nerves  and  occasionally  among  the 
cells  in  the  ventral  horns  of  the  spinal  cord.  The  cells  are  usually 
spherical,  or  nearly  so,  in  shape  and  the  process  close  to  the  cytom 
is  surrounded  by  a  myelin  sheath.  At  a  short  distance  from  the 
cell  the  process  divides  like  a  T  or  Y,  one  process  entering  the  central 
nerve  system   (axone)   and  the  other  extending  to  the  periphery 


164 


PRACTICAL   HISTOLOGY 


(myelinated  dendrite).  Embryologically  these  are  bipolar  cells  in 
which  the  cytom  grew  unequally  so  that  gradually  the  two  processes 
were  thrown  side  by  side;  at  the  same  time  the  cytoplasm  became 
so  extended  as  to  form  the  undivided  portion  of  the  process.  As  a 
result  this  seemingly  unipolar  cell  is  bipolar  functionally. 

Bipolar  cells  are  found  in  the  cochlear  and  vestibular  ganglia 
connected  with  the  corresponding  divisions  of  the  auditory  nerve; 


Fig.  97. — Purkinje  Cell  of  the  Cerebellum.  ' 
a.  Azone;    b,   collateral;  c,  d,  dendrites  and  telodendrites.     (Cajal.) 

in  the  olfactory  mucosa;  as  the  rod  and  cone  cells  of  the  retina;  as 
the  Purkinje  cells  of  the  cerebellum.  Each  possesses  an  axone 
and  a  single  dendrite. 

The  multipolar  cells  are  the  most  numerous  and  are  found  in  the 
cerebral  cortex  and  in  the  gray  substance  of  the  spinal  cord  and 
brain  stem.  These  cells  possess  three  or  more  processes,  one  axone 
and  the  remainder  dendrites. 

Nerve  cells  vary  in  size  from  \\x  to  9^  in  diameter,  for  the  smallest, 


XKKVK     I'lSSTKS 


l65 


to  75/i  to  150/i  for  the  largest.  The  former  are  the  granule  tells  of 
the  cerebellar  cortex  and  the  latter  arc  those  of  the  ventral  horns  of 
the  spinal  cord.  The  next  largest  are  the  large  pyramidal  cells  of  the 
cerebral  cortex  ("giant  cells  of  Betz,"  motor  area).  Nerve  cells 
without  an  axone  are  found  in  the  retina  and  olfactory  bulb.  Neurons 
are  unable  to  reproduce  themselves;  if  the  axone  becomes  destroyed 
it  may  regenerate  but  if  the  cytom  is  destroyed  it  is  never  replaced. 
According  to  the  neurone  theory  the  nerve  system  consists  of  a 
series  of  closely  related  and  physiologically  corelated  elements  from 


Fig.  98. — Synapse  of  the  Investment  Type. 
(Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 


the  central  system  to  the  periphery;  in  other  words  one  neuron  does 
not  extend  from  the  center  to  the  periphery.  At  least  two  and  as 
many  as  six  are  concerned  in  the  various  pathways.  These  related 
neurons  are  not  directly  connected  to  one  another  although  the 
processes  of  one  cell  may  end  around  the  body  of,  or  in  contact  with 
the  processes  of  another  cell.  This  has  been  shown  by  special  stain 
methods,  by  the  study  of  the  nerve  system  in  certain  diseases  and 
injuries  and  by  the  study  of  the  development  of  the  nerve  cells  and 
fibers.  The  cells  and  processes  alike  are  affected  by  degenerative 
processes,  but  the  preceding  or  succeeding  neurons  are  not  affected. 


i66 


PRACTICAL   HISTOLOGY 


The  ramifications  of  the  axone  of  one  cell  about  the  body  of 
another  cell  or  its  processes  constitute  a  synapse.  When  the 
teleneurites  surround  the  cell  body  this  form  of  synapse  is  called  an 
investment;  when  the  teleneurites  come  in  relation  with  the  teloden- 
drites  of  another  cell  this  constitutes  an  interlacement.  Occasionally 
synapses  may  occur  between  the  dendrites  of  two  cells.  Another 
peculiar  form  of  synapse  is  that  in  which  the  axone  does  not  branch 
at  its  termination  but  ends  in  a  bulb-like  enlargement  upon  the 
body  of  another  cell,  as  in  the  trapezoid  and  ventral  acoustic  nuclei 
of  the  brain  stem. 

The  neuroglia,  or  glial  substance,  is  the  peculiar  supportive 
tissue  of  the  nerve  system.     Like  the  nerve  cells  it  is  of  ectodermal 


Fig.  99. — Spider  Glial  Cell. 

{After  Andriezen.) 


Fig.  100. — Mossy  Glial  Cell  in 
Relation  with  a  Capillary. 
{After  Andriezen.) 


origin.  Unlike  the  intercellular  substance  of  other  tissues  it  is 
not  the  result  of  the  activity  of  the  functionating  (nerve)  cells  but 
the  glial  substance  itself  consists  of  cells  and  intercellular  substance. 
The  glial  cells  give  rise  to  the  glial  fibers. 

Glial  cells  are  of  two  kinds  ependymal  cells  and  astrocytes.  The 
ependymal  cells  are  apparently  some  of  the  original  elements  of  the 
neural  tube.  They  represent  the  remainder  of  those  indifferent 
cells  that  gave  origin  to  the  neuroblasts  and  spongioblasts.  They 
are  simple  ciliated  cells  that  are  found  lining  the  canal  of  the  spinal 
cord  and  parts  of  the  ventricles  of  the  brain.  The  basal  ends  of  the 
cells  are  usually  branched;  these  branches  extend  into  the  surround- 
ing gelatinous  substance  where  they  soon  disappear.     These  cells 


NERVE   TISSUES 


167 


multiply  in  the  adult  body  and  tend  to  occlude  the  spinal  canal  in 
part  or  as  a  whole. 

The  astrocytes  are  usually  stellate  elements  with  many  processes. 
The  mossy  cells  are  those  in  which  the  processes  are  short  and  thick 
and  are  found  chiefly  in  the  gray  nerve  tissue.  In  some  of  the  cells 
the  processes  are  dendritic  and  do  not  extend  far  from  the  cell.     The 


?<  yqt  a, 

Fig.  ioi. — Cross-section    of  Spinal  Cord  Showing  Glial  Fibers  Among 

the  Nerve  Fibers. 

a,  a,  Glial  fibers;  a',  same  cut  across;  n,  body  of  glial  cell;  /,  cross-section  of  a 
myelinated  nerve  fiber;  a,  axone  of  same;  /',  small  (sensor?)  nerve  fiber. 
(Schafer  after  Ranvier.) 


spider  cells  have  fewer  but  longer  processes  and  are  found  mainly  in 
the  white  nerve  tissue.  These  cells  are  both  small  and  large;  the 
smaller  ones  show  merely  a  rim  of  cytoplasm  around  the  deeply  stain- 
ing nucleus.  In  the  larger  cells  the  cytoplasm  is  greater  in  quantity 
and  the  processes  are  said  to  be  more  numerous. 

The  glial  fibers  are  delicate  filaments  of  protoplasm  that  form  a 
network  for  the  support  ofthe  nerve  cells  and  glial  cells.  Some  of 
the  fibers  have  a  very  intimate  relation  with  the  glial  cells  passing 


1 68  PRACTICAL   HISTOLOGY 

close   to   the  cell-body   or   even  through  its  peripheral  cytoplasm 
although  they  are  distinct  from  the  cell-body. 

According  to  the  investigations  of  Hardesty  the  glial  fibers  appear 
late,  that  is  after  some  of  the  nerve  fibers  have  become  myelinated 
and  long  after  the  first  connective  tissue  fibers  have  appeared. 
They  are  formed  in  the  neural  syncytium  (neurospongium)  in  which 
they  are  formed  directly  by  the  cells  or  through  their  activity. 

The  white  nerve  substance  of  the  central  nerve  system  consists 
of  myelinated  nerve  fibers  supported  by  neuroglia  and  some  white 
fibrous  connective  tissue;  the  latter  is  chiefly  for  the  support  of  the 
blood-vessels.  In  the  peripheral  nerves  the  supportive  substance  is 
white  fibrous  tissue. 

After  the  axone  of  a  cell  of  the  first  type  leaves  the  cell  it  becomes 
a  nerve  fiber.  If  the  axone  becomes  invested  with  a  myelin  sheath 
it  is  then  a  myelinated  nerve  fiber  such  as  constitute  the  cere- 
brospinal system.  If  no  myelin  sheath  is  present  it  is  then  called 
an  amyelinated  nerve  fiber,  as  is  seen  in  the  sympathetic  nerve 
system. 

An  amyelinated,  or  nonmedullated  nerve  fiber  (Remak's  fiber) 
consists  of  an  axis  cylinder  surrounded  by  a  delicate  sheath  called 
the  neurolemma,  and  is  said  to  be  connected  exclusively  with  the 
sympathetic  nerve  system.  Ransom,  however,  found  that  these 
fibers  were  more  numerous  in  the  ordinary  nerves  than  had  hitherto 
been  supposed.  These  fibers  are  very  numerous  in  the  spinal  nerves, 
and  in  the  vagal  nerves  of  the  dog  the  amyelinated  fibers  predominate 
caudal  to  the  diaphragm;  these  fibers  are  both  efferent  and  afferent. 

The  axone  arises  at  the  axis  cylinder  hillock  and  consists  of  a 
bundle  of  neurofibrils  imbedded  in  apparently  homogeneous 
neuroplasm.  It  is  continuous  in  its  course  and  terminates  in  a 
set  of  branches  called  telencurites.  These  sympathetic  axones  are 
the  smallest  measuring  from  1.8  to  3.6  microns  in  diameter.  The 
neurofibrils  seem  to  converge  from  the  dendrites  to  the  axis-cylinder 
hillock.  Although  some  investigators  claim  that  these  neurofibrils 
branch  and  interlace  in  the  nerve  fiber  most  observers  hold  that  they 
are  individual  throughout  their  course.  These  fibers  are  semi-solid 
and  readily  become  varicose.  Under  high  magnification  each  fibril 
seems  to  be  tubular  in  character,  the  center  of  the  tubule  begin 


NERVE    l  [SSTJ]  -  [69 

filled  with  the  fluid  conductive  substance,  as  pointed  out  by  Carlson. 
Surrounding  the  axone  there  \s  a  delicate  sheath  that  may  be  more 
pronounced  in  places  and  contain  nuclei.  This  is  the  neurolemma. 
It  is  not  always  well  developed  and  its  nuclei  appear  to  be  imbedded 
in  the  peripheral  portion  of  the  axone. 

The  amyelinated  nerve  fibers  are  grayish  in  color.  They  ter- 
minate in  the  smooth  muscles  of  the  various  organs  (including  the 
heart)  and  upon  the  epithelial  cells  of  mucous  membranes  and  glands. 
These  fibers  are  also  seen  in  several  of  the  cerebral  nerves  and  the 
ventral  roots  of  the  thoracic,  most  of  the  lumbar  and  some  of  the 
sacral  spinal  nerves.  Through  these  they  go  to  or  come  from  the 
various  organs  and  structures  to  which  these  nerves  are  distributed. 

Amyelinated  nerve  fibers  without  a  neurolemma  consist  of  merely 
a  naked  axis  cylinder.  The  fibers  of  the  olfactory  nerves  belong 
to  this  class.  Here  are  also  placed  the  proximal  and  distal  parts  of 
the  myelinated  type  that  have  as  yet  not  become  invested  with 
this  sheath  or  have  lost  it.  It  seems  that  this  is  a  very  trifling 
distinction  as  no  myelinate  nerve  fiber  receives  its  sheath  directly 
upon  arising  from  the  cytom  nor  does  the  sheath  ever  continue 
to  the  termination  of  the  axis  cylinder. 

A  myelinated,  or  medullated  nerve  fiber  is  white  in  color  and 
forms  the  bulk  of  the  white  nerve  tissue  of  the  cerebrospinal  system; 
some  of  this  variety  are  found  even  in  sympathetic  nerves.  This 
type  of  fiber  consists  of  axone,  myelin  sheath  and  neurolemma.  The 
axone  consists  of  a  bundle  of  neurofibrils  imbedded  in  a  mass  of 
homogeneous  neuroplasm,  apparently  surrounded  by  a  delicate 
membrane  called  the  axilemma.  The  presence  of  this  membrane 
is  denied  by  some.  These  fibrillse  are  probably  the  conductive 
parts  of  the  fiber  though  some  are  inclined  to  believe  that  the  neuro- 
plasm only  has  this  property.  The  fibrils  in  mammals  are  very  fine 
and  almost  evenly  distributed  in  the  axone  although  occasionally 
a  narrow-  peripheral  clear  zone  may  be  found.  In  lower  animals 
the  fibrils  are  coarser  and  tend  to  form  a  mass  in  the  center  of  the 
axone  with  a  resulting  clear  peripheral  area.  The  fibrils  are  con- 
sidered by  some  merely  a  support  for  the  neuroplasm.  The  largest 
axones  (to  the  skeletal  muscles)  are  8  to  16  microns  in  diameter,  though 
sensor  fiber  may  be  as  small  as  4  microns  in  diameter. 


i7° 


PRACTICAL  HISTOLOGY 


The  myelin,  or  medullary  sheath  {white  substance  of  Schwann)  is, 
apparently  an  insulating  sheath  found  mainly  in  the  cerebrospinal 
system.  This  sheath  is  not  continuous  but  is  interrupted  at  regular 
intervals  called  the  nodes  of  Ranvier.  In  fresh  nerve  fibers  this 
sheath  is  homogeneus.  After  fixation  it  consists  of  a  reticular  sub- 
stance and  the  myelin.  The  former  is  composed  of  neurokeratin 
and  is  arranged  in  the  form  of  a  network  that  is  invisible  in  fresh 
nerves.  It  seems  to  be  a  coagulation  product  as  the  meshes  of  the 
reticulum  vary  in  size  according  to  the  strength  of  the  reagentused. 


Fig.  102. — Cross-section  of  Osmicated  Nerve. 
(Photograph.     Obj.   16  mm.,  oc.   10  X.) 


Alchohol  and  ether  produce  the  best  results  and  these  results  may  be 
obtained  with  isolated  myelin.  Picric  acid  produces  a  different 
coagulation  effect.  When  this  agent  has  been  used  and  transverse 
sections  are  made  the  myelin  sheath  has  the  appearance  of  fine 
delicate  rods  radiating  from  the  axis  cylinder  to  the  neurolemma. 
The  myelin  substance  is  a  phosphorized  fat  that  is  practically  liquid 
at  the  ordinary  temperatures  for  if  the  neurolemma  of  a  fresh  fiber 
be  ruptured  the  myelin  oozes  out  in  the  form  of  droplets.  This 
substance  responds  readily  to  osmic  acid  solutions   which  turn  it 


NERVE   TISSUES 


171 


black,  thus  showing  the  presence  of  a  fatty  substance.  It  is  also 
readily  soluble  in  ether.     It  is  probably  nutritive  in  function. 

In  the  degeneration  of  nerve  fibers  the  myelin  sheaths  show  the 
first  signs.  This  is  of  importance  in  the  study  of  diseases  of  the 
nerve  system  and  in  tracing  the  fiber  tracts. 

At  regular  intervals  the  myelin  sheath  is  interrupted  and  the  neuro- 
lemma dips  into  the  axis  cylinder.  These  regions  are  the  constric- 
tions of  Ranvier  and  because  the  myelin  sheath  at  these  points  may 


Fig.  103. — Longitudinal  Section  of  Osmicated  Nerve,     a,  Node  of  Ranvier. 
(Photograph.     Obj.  4,  mm.  oc.  5  X). 

be  somewhat  bulbous,  giving  a  nodal  appearance,  they  are  also 
called  the  nodes  of  Ranvier.  These  are  seen  only  in  longitudinal 
sections  of  osmicated  nerve  fibers.  If  a  nerve  fiber  be  treated  with 
nitrate  solution  (Ranvier's  method)  the  solution  penetrates  at  these 
nodes  and  makes  a  -{--like  stain.  Those  portions  between  the  nodes 
are  called  the  intemodes.  In  osmicated  preparations  oblique,  cleft- 
like spaces  are  numerous;  these  are  the  clefts  of  Lantermann  {lines 
of  Schmidt-La ntermann).  The  intervening  parts  of  the  sheath  are 
the  medullary  segments.     What  they  represent  is  still  unsettled. 


172  PRACTICAL   HISTOLOGY 

The  neurolemma,  or  sheath  of  Schwann  is  the  delicate  sheath  that 
limits  the  fiber.  This  is  a  thin,  homogeneous  membrane  and  in  each 
internode  there  is  a  nucleus.  Although  the  sheath  seems  continuous 
over  the  nodes  it  is  though  that  it  really  ceases  here  and  that  the 
successive  nucleated  segments,  constituting  individual  cells,  are 
connected  by  intercellular  cement,  as  is  seen  in  epitheliod  cells. 
This  sheath  probably  represents  specialized  ectodermal  cells  of  the 
neural  tube. 

This  type  of  nerve  fibers  is  found  in  the  peripheral  nerve  system. 

Myelinated  nerves  without  a  neurolemma  are  found  in  the  brain 
and  spinal  cord.  All  of  the  white  substance  consists  of  nerves  of 
this  type.  In  these  fibers  the  myelin  sheath  possesses  no  nodes  of 
Ranvier  and  so  continues  uninterruptedly.  Sheath  cells  are  present 
and  these  are  said  to  assist  in  the  production  and  maintenance  of  the 
myelin.  Myelinated  nerve  fibers  conduct  impulses  more  rapidly 
than  the  amyelinated  fibers. 

THE  PERIPHERAL  NERVE  SYSTEM 

The  peripheral  nerve  system  comprises  the  nerves  and  the  ganglia 
connected  with  the  spinal  and  the  sensor  cerebral  nerves. 

A  nerve  or  nerve  trunk  consists  of  a  variable  number  of  nerve 
fibers  collected  into  a  compact  mass  and  bound  together  by  various 
sheaths.  Upon  the  outside  is  a  sheath  of  loose  areolar  tissue  called 
the  epineurium.  This  contains  the  larger  vessel  and  lymphatics 
and  also  the  nervi  nervorum,  the  sensor  nerves  of  the  nerves.  The 
epineurium  is  usually  thin  and  sends  in  septa  (for  the  support  of 
blood-vessels)  that  divide  the  nerve  into  large  secondary  bundles; 
from  these  septa  others  extend  in  to  surround  individual  bundles 
of  nerve  fibers  called  funiculi.  The  sheath  surrounding  each 
funiculus  is  called  the  perineurium  and  this  is  usually  thicker  in 
proportion  than  the  epineurium.  Although  the  perineurial  sheaths 
seem  compact  their  layers  are  readily  separable  from  one  another, 
indicating  extensive  tissue  or  lymph  spaces  that  are  continuous  with 
the  spaces  around  the  brain  and  spinal  cord.  By  this  means  the 
cerebrospinal  fluid  may  pass  into  the  nerves  toward  the  periphery 
(Keyes).     From  the  perineurial  sheath  bundles  of  fibers  pass  into 


NERVE    TISSUES 


173 


each   fasciculus  forming  here  a  delicate   reticulum    [endoneurium) 

which  supports  not  only  the  nerve  fibers  but  also  the  capillaries 
that  nourish  the  nerve  trunk.  The  endoneurium  may  even  form 
partial  septa. 

The  funiculi  as  well  as  the  nerves  vary  greatly  in  size.  A  nerve, 
as  the  optic  nerve,  may  consist  of  a  single  funiculus  comprising  450,- 
000  to  800,000  fine  nerve  fibers, 
or  it  may  consist  of  many  funiculi 
but  few  fibers,  as  the  vagal  nerve 
with  its  10,000  nerve  fibers.  The 
nerve  fibers  in  a  funiculus  rarely 
branch  but  the  fibers  themselves 
may  start  in  one  funiculus  and 
cross  over  and  join  another. 
When  a  single  nerve  fiber  runs 
individually  to  an  organ  it  is 
usually  surrounded  by  a  delicate 
sheath  derived  from  the  perineu- 
rium, called  the  sheath  of  Henle. 

Nerves  are  quite  vascular.  The 
large  arteries  enter  the  epineurium 
and  divide  into  branches  that  pass 
to  the  septa  betwreen  the  secondary 
bundles;  from  here  branches  are 
sent  into  the  primary  fasciculi 
where  the  arterioles  form  an  ex- 
tensive capillary  plexus  in  the 
endoneurium.  The  blood  is  col- 
lected by  the  venules  in  the  endoneurium  and  from  here  is  conducted 
by  small  venous  channels  that  lie  along  side  of  the  arterial  channels. 

The  lymph  spaces  of  the  nerve  are  very  extensive  as  has  been 
mentioned.  Perivascular  lymph  vessels  are  said  to  be  numerous  in 
the  epineurium  and  larger  septa. 

The  nervi  nervorum  are  numerous  and  small.  They  supply  the 
blood-vessels  (sympathetic)  and  some  are  sensor  in  function.  The 
presence  of  the  latter  nerves  is  denied  by  some. 

A  ganglion  is  an  isolated  mass  of  nerve  tissue  in  the  course  of  a 


Fig.  104. — Cross-section  of  a 
Human  Sciatic  Nerve. 
A,   Epineurium;  B,  funiculus  of  nerve 
fibers;    C,   Perineurium.      (Radasch, 
Reference  Handbook  of  the  Medical 
Sciences.) 


174 


PRACTICAL  HISTOLOGY 


sensor  nerve.  Some  consist  of  merely  a  few  nerve  cells  and  are,  there- 
fore, microscopic;  others  are  quite  large  and  are  easily  found  and 
recognized.  The  cerebrospinal  ganglia  all  have  the  same  general 
structure. 

A  ganglion  consists  of  a  sheath  or  capsule  of  white  fibrous  tissue 
that  supports  the  structures  within  and  serves  to  delimit  it  from  the 

surrounding  structures  so  that 


it  may  be  readily  isolated. 
This  sheath  sends  in  trabecular 
that  form  a  delicate  network 
in  which  are  found  the  ganglion 
cells,  myelinated  and  amyeli- 
nated  nerve  fibers,  blood-ves- 
sels and  lymphatics.  The  cells 
of  the  cerebrospinal  ganglia 
are  usually  ovoid,  or  round  and 
of  the  unipolar,  or  bipolar  type. 
The  unipolar  cell  is  now  looked 
upon  as  bipolar  as  the  single 
process  is  considered  merely 
an  extension  of  the  cytoplasm 
and  not  a  mere  process.  The 
cells  of  the  vestibular  and 
cochlear  ganglia  of  the  acoustic 
nerve  retain  their  bipolar  char- 
acter throughout  life.  The 
nerve  cell  is  surrounded  by  a 
lymph  space  that  is  limited  by 
a  single  layer  of  flattened  epi- 
theliod  cells  that  is  extended 
upon  the  processes  and  is  con- 
tinuous with  the  neurolemma. 

The  spaces  and  capsules  are  absent  in  the  vestibular  and  cochlear 

ganglia. 

There  are  three  types  or  varieties  of  cells  in  the  spinal  ganglia:     (i) 

Large  unipolar  cells  with  thick  processes  that  branch  Y-  or  T-like 

become    myelinated    and    leave    the   ganglion    (first   type   cells). 


Fig.  105. — Section  of  Semilunar 
Ganglion  of  a  Horse.  The  nucle- 
olus shows  up  well  in  several  of  the  cells. 
(Photograph.  Obj.  i6mm.,oc.  7.5  X.) 


NERVE   TISSUES 


175 


(2)  Cells  of  the  second  type  in  which  the  delicate  axones  remain  in 
the  ganglion  and  divide  into  fine  branches  that  penetrate  the  epi- 
theliod  capsules  and  terminate  about  the  previous  cells.  (3)  Small 
cells  of  pyriform  shape  the  process  of  which  divides  and  leave  the 
ganglion  as  in  the  first  variety.  The  processes  of  these  last  cells 
do  not  become  myelinated  however  and  Ransom  believes  them  to  be 
efferent  in  function.  These  amyelinated  fibers  are  the  ones  previously 
mentioned  as  components  of  spinal  nerves.  In  lower  animals  these 
last  cells  constituted,  according  to  Ransom,  two-thirds  of  the  cells 
of  the  ganglion.  A  few  multipolar  cells  are  found  in  ganglia  of  the 
adult  according  to  Dogiel. 


Fig.  106. — Three  Small  Ganglia  of  the  Submucous  Plexus.  A,  A  nerve 
fiber  passing  through  one  of  the  ganglia  but  giving  off  collaterals  to  it. 
(After  Cajal.) 

The  nerve  fibers  are  myelinated  and  amyelinated.  The  former  are 
afferent  and  efferent.  The  afferent  fibers  come  from  the  outside  and 
terminate  in  the  ganglion  in  delicate  branches  that  penetrate  the 
capsules  of  the  cells  and  form  an  arborization  about  the  bodies  of 
the  ganglion  cells.  The  efferent  fibers  are  those  that  arise  from  the 
first  type  cells  (1  and  3).  In  the  case  of  the  axones. of  cells  (1)  they 
form  a  convoluted  mass  before  leaving  the  cell  capsule  and  after 


176  PRACTICAL   HISTOLOGY 

passing  through  the  capsule  soon  become  myelinated.  The  axones 
of  cells  (3)  run  a  straight  course  and  do  not  become  myelinated. 
Other  amyelinated  fibers  are  those  of  the  sympathetic  system  and 
the  axones  of  cells  (2). 

In  sympathetic  ganglia  the  cells  are  multipolar  in  form.  There 
are  two  types  of  cells.  (1)  Large  spherical  elements  that  possess 
from  1  to  16  dendrites.  The  axones  of  these  cells  pass  to  a  nerve  as 
a  nonmedullated  fiber  but  may  later  receive  a  delicate  myelin  sheath. 
These  are  considered  sensor  in  function.  The  dendrites  are  slender, 
long,  enter  the  nerve  and  probably  pass  to  a  neighboring  ganglion. 


Fig.   107. — Perivascular  Terminal  Nerve  Plexuses  of  the  Sympathetic 

Nerve  System.     {After  Dogiel.) 


(2)  Smaller  stellate,  or  spindle-shaped  cells  with  5  to  20  dendrites. 
The  axone  is  also  amyelinated  when  it  enters  the  nerve  but  may  later 
receive  a  delicate  myelin  sheath.  The  dendrites  are  short  and  thick 
and  form  synapses  about  other  cells  of  the  same  ganglion.  These 
are  motor  cells.  The  corpuscles  of  Nissl  are  of  medium  size  and  are 
grouped  near  the  periphery  of  the  cell. 

The  fibers  in  a  sympathetic  ganglion  are  both  myelinated  and  amye- 
linated. The  former  are  derived  from  the  cerebrospinal  system  and 
constitute  the  white  rami  communicantes  while  the  latter  are  the 
sympathetic  fibers  proper. 

Sympathetic  nerves  have  the  same  general  structure  as  those  of  the 
cerebrospinal  system  but  the  sheaths  are  usually  thinner  and  the  nerves 
smaller.  In  the  larger  nerves  are  found  many  myelinated  fibers 
that  are  derived  from  the  cerebrospinal  system. 


NERVE   TISSUES  1 77 

Degeneration  and  Regeneration  of  Nerves. — If  a  living  nerve  be 
cut  union  between  the  cut  parts  is  reestablished  by  cicatricial  tissue 
but  the  cut  libers  themselves  do  not  unite.  The  peripheral  or 
distal  portion  of  the  process  undergoes  degeneration  within  twenty- 
four  hours  after  the  lesion,  in  warm-blooded  animals  but  the  changes 
are  later  in  cold-blooded  animals.  The  neurolemma  becomes 
quite  distinct,  its  nuclei  increase  in  size;  the  myelin  sheath  under- 
goes changes  and  droplets  of  fat  become  abundant.  The  axis 
cylinder  undergoes  disintegration  and  disappears.  The  myelin 
is  almost  entirely  removed  (probably  by  the  action  of  phagocytes) 
but  fatty  granules  in  the  neighboring  cells  increase  and  stain  more 
deeply  with  osmic  acid  solution  than  the  normal  myelin.  This 
process  is  not  limited  to  one  part  of  the  axone  but  occurs  along  its 
whole  length  at  the  same  time.  This  change  occurs  earlier  in  the 
motor  than  in  the  sensor  nerves. 

The  proximal  portion  (cell  end)  of  the  axone  does  not  degenerate 
but  regenerates.  After  the  lesion  the  cut  end  usually  becomes 
slightly  swollen.  The  regeneration  process  is  slow  as  changes  are  not 
noticed  until  nearly  two  months  have  elapsed.  If  the  nerves  be 
then  removed  and  sections  made  then  the  old  neurolemmal  tubes 
will  be  found  to  contain  new  axones,  and  new  fibers,  individual  or 
in  groups,  are  seen  between  these.  These  new  fibers  may  be  amye- 
linated  or  possess  a  thin  myelin  sheath.  These  fibers  are  seen  to  be 
continuous  with  the  proximal  ends  of  the  original  nerve  fibers.  The 
small  groups  noted  may  be  the  outgrowth  of  only  one  axis  cylinder, 
or  only  one  or  two  may  arise  from  one  axone  but  these  will  then 
branch  and  rebranch  until  quite  a  number  has  been  formed.  As  a 
result  there  are  more  fibers  in  the  healed  nerve  than  in  the  original 
condition.  The  new  fibers  arise  from  the  old  one  near  a  node  and 
may  enter  the  old  neurolemmal  sheathes  or  be  independent  of  these. 
In  the  latter  case  they  are  at  first  amyelinated  and  later  become  mye- 
linated and  receive  a  neurolemma.  The  growing  cut  ends  of  the 
axones  are  bulbous  and  resemble  the  growing  axonic  process  of  the 
neuroblast.  As  this  growth  is  slow,  the  function  of  the  nerve  is  not 
resumed  for  many  months  after  the  lesion  and  only  a  few  of  the 
many  new  fibers  assume  the  function  of  the  fibers  cut. 

The  new  axones  that  do  not  enter  the  old  sheath  have  a  very  ir- 
12 


i78 


PRACTICAL  HISTOLOGY 


regular  course.  This  is  probably  due  to  the  fact  that  they  have  no 
original  path  to  follow  and  must  sort  of  seek  their  way.  Regenera- 
tion occurs  more  quickly  if  the  cut  ends  are  placed  in  apposition. 
If  a  gap  is  left  the  process  is  slower.  If  a  piece  of  the  nerve  be  re- 
moved and  the  cut  ends  cannot  be  brought  together  then  a  piece  of 
guide  material  should  be  placed  in  the  gap.  The  best  material  is 
a  piece  of  aseptic,  dead  nerve  (Huber). 

NERVE  ORGANS 


Nerve  fibers  terminate  either  in  the  form  of  telodendrites  (free) 

or  in  some  special  structure  called  a  nerve  organ;  these  may  be 

comparatively  simple  or  very  complex.     There  are  two  varieties 

of  organs  sensor  and  motor. 

The  sensor  organs  are  free,  tactile  cells,  corpuscles  and  spindles. 

The  free  terminals  are  found  in  mucous  membranes  (especially 

in  stratified  epithelium),  serous  mem- 
branes, cornea,  skin  and  intermuscular 
connective  tissue.  As  the  myelinated 
nerve  fibers  approach  their  termination 
they  branch.  In  the  epithelial  struc- 
ture when  the  basement  membrane  is 
reached  the  neurolemma  and  myelin 
sheathes  disappear  and  the  naked  axone 
enters  the  epithelial  layer.  In  this  the 
terminal  fibrillar,  which  are  usually 
varicose,  end  in  leaf-like  expansions,  or 
bulb-like  enlargements  upon  the  epi- 
thelial cells  but  not  within  them.  In 
serous  membranes  and  in  the  inter- 
muscular septa  the  fibrils  end  in  flat- 
tened expansions. 
Tactile  Cells  Are  Simple  and  Compound. — The  simple  variety 
consists  of  modified  epithelial  cells,  each  of  which  is  composed  of 
a  disc-like  structure,  6  to  13  microns  in  diameter,  and  a  mass 
of  clear  cytoplasm.  In  each  disc  a  naked  nerve  fiber  (dendrite) 
terminates.     These  structures  are  found  within  the  interpapillary 


Fig.  108. — Vertical  Section 
of  Skin  of  Great  Toe  of 
a  Man. 

A.  Epidermis.  B.  derma,  a, 
tactile  cell;  b,  tactile  menis- 
cus; c,  nerve  fiber;  d,  con- 
nective tissue  sheath  of 
same;  x,  tactile  cells  in 
derma.    (Stohr's  Histology.) 


NERVE   TISSUES 


179 


portions  of  the  epithelium  of  the  skin  and  in  the  root  sheaths  of 
the  hairs. 

The  compound  tactile  cells  consist  of  two  or  more  discs  containing 
between  them  tactile  cells  which  are  nucleated  masses  of  granular 
protoplasm.     See  Grandys  Corpuscles. 


Fig.  109. — Simple   Tactile   Cells  in  the  Epithelium  of   a   Pig's   Snout. 

{After  Ranvier). 

The  tactile  corpuscles  or  bulbs  are  the  more  differentiated  of 
these  organs.  They  vary  in  complexity  from  the  comparatively 
simple  genital  and  conjunctival  corpuscles  to  the  more  complex 
corpuscles  of  Meissner  and  Vater. 


Fig.  1 10. — Compound  Tactile  Cells,  with  Two  and  Three  Cells,  From  a 
Duck's  Tongue.     {After  Izquierdo.) 


The  conjunctival  corpuscles  or  bulbs  are  spherical,  oval,  or  pear- 
shaped  bodies  in  which  the  cells  are  not  regularly  arranged.  The 
nerve  fibers,  upon  piercing  the  structure  become  amyelinated  and 
pass  through  a  central  core  of  homogeneous  protoplasm  and  termi- 
nate in  a  bulbous  manner.     The  core  is  surrounded  by  a  capsule  that 


i  So 


PRACTICAL   HISTOLOGY 


is  composed  of  flattened  cells.  These  organs  average  from  60  to 
400  microns  in  length  and  may  have  as  many  as'  10  nerve  fibers 
connected  with  one  organ. 

The  genital  corpuscles  or  bulbs  are  more  complex.  Each  is 
divided  into  two  to  six  knob-like  parts.  The  nerve  fiber  enters 
the  organ  and  divides  into  numerous  branches  each  of  which  passes 
to  a  segment;  here  it  may  continue  undivided,  or  form  a  series  of 
branches.  These  are  surrounded 
by  the  capsular  cells.  These 
measure  from  60  to  400  microns 
in  length  and  40  to  100  microns 
diameter.  They  are  found  in 
the  mucosa  of  the  glans  penis, 
glans  clitoris  and  neighboring 
structures. 


Fig.  hi. — Bulbous  Corpuscle 
from  the  Human  Conjunctiva. 
Methylene  Blue  Stain.  {After 
Dogiel,  from  Bohm  and  Von 
Davidoff.) 


Fig.  112. — Genital  Corpuscle  from 
the  Human  Glans  Penis.  Methy- 
lene Blue  Stain.  {After  Dogiel, 
from  Bohm  and  von  Davidoff.) 


Other  end  bulbs  both  simple  and  complex  are  found  in  the  perito- 
neum, around  joints,  in  tendons  and  ligaments  and  even  in  nerves. 

The  corpuscles  of  Rufrini  are  cylindrical  structures  consisting  of 
a  central  core  of  connective  tissue,  or  according  to  some,  granular 
material.  This  is  surrounded  by  a  sheath  of  connective  tissue.  The 
nerve  fiber  usually  enters  from  the  side,  loses  its  sheath  of  Henle 
and  within  the  structure  becomes  a  naked  process  that  forms  a 
close  ramification  of  fibrils  around  the  connective  tissue  bundles, 
or  in  the  granular  material.  One  original  nerve  fiber  may  supply  a 
number  of  these  organs.     These  are  found  in  the  deeper  portion  of 


NERVE    TISS1   ES 


181 


the  stratum  reticulare  of  the  skin  and  are  about  as  numerous  as 
the  Pacinian  corpuscles. 

The  corpuscles  of  Golgi-Mazzoni  are  cylindrical,  or  spherical 
organs  and  consist  of  a  large  granular  core  surrounded  by  a  capsule  of 
connective  tissue  that  consists  of  a  number  of  layers.  As  the  nerve 
fiber  penetrates  the  structure  the  sheaths  blend  with  the  capsule 
and  the  naked  process  enters  the  granular  core  and  divides  into  a 
number  of  branches  that  terminate  in  flattened 
expansions.  These  are  found  in  the  derma  of 
the  external  genitalia,  the  fingers  and]  in_tthe 
periosteum  and  conjunctiva. 

The  corpuscles  of  Grandy  are  really  compound 
tactile  cells.  Each  consists  of  a  capsule  of  white 
fibrous  tissue  surrounding  two  or  more  tactile 
epithelial  cells.  These  cells  are  flattened  and 
their  cytoplasm  is  striated.  Between  the  cells 
are  the  tactile  discs.  When  the  nerve  fiber 
enters  the  organ  the  sheaths  are  lost  upon 
entering  or  by  the  time  it  has  passed  through 
the  capsule.  The  naked  axone  then  divides 
into  as  many  branches  as  there  are  discs  and  one 
branch  ends  in  each  disc  in  a  series  of  fibrils, 
which  according  to  Dogiel,  enter  the  adjoining 
cells.  These  organs  are  found  only  in  the 
aquatic  birds. 

The  corpuscles  of  Herbst  resemble  some- 
what the  Pacinian  corpuscles.  Each  consists  of  a  capsule  in 
which  the  outer  layers  run  longitudinally  and  the  inner  ones 
transversely.  The  core  is  composed  of  transversely  placed  cells 
and  it  is  traversed  by  the  naked  axone.  These  organs  are  found 
in  the  cere  of  aquatic  birds. 

The  tactile  corpuscles  of  Meissner  are  more  complex.  Each 
measure  about  ioo  to  180  microns  in  length  and  35  to  50  microns 
in  diameter.  It  consists  of  a  capsule  of  white  fibrous  connective 
tissue  that  encloses  a  number  of  flattened  masses  of  protoplasm 
with  transversely  placed  nuclei.  One  or  more  nerve  fibers  is  con- 
nected with  each  organ  and  upon  contact  with  the  corpuscle  the 


Fig.  113.  —  Cor- 
puscle of  Meiss- 
ner from  Great 
Toe  of  Man. 

n,  Myelinated  nerve 
fiber;  h,  connec- 
tive tissue  sheath; 
e,  varicosities. 
The  nuclei  are 
invisible.  (Stohr's 
Histology.) 


182 


PRACTICAL   HISTOLOGY 


neurolemma  is  lost.  The  myelin  sheaths  soon  leave  and  the 
naked  axones,  after  a  spiral  course,  divide  into  a  number  of  varicose 
fibrils  that  form  a  network  and  then  terminate  in  small  bulbous 
enlargements  near  the  capsule.  These  are  found  throughout  the 
skin  of  the  body  but  are  most  numerous  in  the  derma  of  the  palmar 
surface  of  the  finger  tips  (as  many  as  twenty  to  the  square  milli- 
meter). They  are  also  found  in  the 
derma  of  the  plantar  surface,  in  the 
nipples,  lips,  glans  clitoris  and  penis 
and  the  conjunctiva.  They  convey 
sensations  of  pain,  pressure,  warmth 
and  cold.  It  is  said  that  two  sets  of 
sensor  fibers  enervate  them,  one  for 
light  pressure  and  light  temperature 
changes  and  the  other  for  pain  and 
extreme  temperature  changes. 

Pacinian  corpuscles  (Vater)  are 
also  called  lamellar  corpuscles. 
Each  consists  of  a  capsule,  inner 
bulb  and  end  knob.  The  capsule 
consists  of  lamellae  of  connective 
tissue  concentrically  arranged  and 
which  are  usually  bound  together  by 
an  intracapsular  ligament.  These 
lamellae  are  from  forty  to  sixty  in 
number  and  the  outer  ones  are  more 
widely  separated  from  one  another 
than  the  inner  ones.  Each  lamella  is  said  to  consist  of  both 
white  fibrous  and  elastic  tissues  and  is  covered  upon  both  surfaces 
by  endothelial  cells  forming  a  series  of  lymph  spaces. 

The  inner  bulb,  or  core,  is  a  cylindrical  mass  of  protoplasm  that 
may  show  striations  and  nuclei.  It  is  thought  to  consist  externally 
of  flattened  nucleated  cells  surrounding  the  more  homogeneous 
central  portion.  A  single  nerve  fiber  enters  each  corpuscle.  As  it 
pierces  the  capsule  the  neurolemma  blends  therewith  and  the  myelin 
sheath  is  lost  when  the  inner  bulb  is  reached.  The  naked  axone, 
showing  its  fibrillation,  in  properly  stained  sections,  passes  through 


Fig.  114. — A  Tactile  Corpuscle 
with  its  Cells  and  Ter- 
minal    Neurofibrils. 

a,  Axone.     {After  Van  de  Velde.) 


NERVE   TISSUES 


l83 


the  core  at  the  end  of  which  it  expands  into  knob-like  structure, 
the  end  knob.  In  this  the  terminal  fibrils  form  a  very  dense  mesh- 
work.  If  the  axone  divides  in  the  core  the  latter  also  divides.  A 
small  amyelinated  nerve  fiber  has  been  found  by  Solokoff,  passing 
to  the  core  and  terminating  upon  it  in  a  reticular  manner. 

A  small  artery  and  vein  accompany  the  nerve  into  the  corpuscle. 
The  artery  forms  capillary  vessels  that 
form  loops  between  the  lamellae;  one 
capillary  accompanies  the  inner  bulb  and 
courses  along  the  outer  surface  of  this  for 
a  variable  distance.  The  blood  is  returned 
by  a  small  vein  that  leaves  at  the  nerve 
entrance. 

These  organs  are  visible  to  the  unaided 
eye,  measuring  usually  2.5  mm.  in  length 
and  1  mm.  in  diameter.  They  are  found 
in  the  deep  part  of  the  derma,  along 
tendons,  around  joints,  in  the  peritoneum, 
in  the  mesentery  (especially  in  lower 
animals)  and  in  the  pancreas  of  the  cat. 

Muscle  Spindles. — These  organs  are 
spindle-shape  and  consist  of  from  4  to  20 
small  voluntary  muscle  fibers,  the  intra- 
fusal fibers,  surrounded  by  a  delicate  white 
fibrous  sheath  called  the  axial  sheath. 
External  to  this  is  the  capsule  composed 
of  about  six  layers  of  white  fibrous  con- 
nective tissue  concentrically  arranged  and  separated  from  the 
axial  sheath  by  a  lymph  space.  In  the  equatorial  region  of  the 
organ  the  muscle  fibers  consist  chiefly  of  sarcoplasm  and  the  stria- 
tions  are  faint,  while  at  the  ends  the  striations  are  quite  distinct. 
The  muscle  fibers  are  said  to  pass  into  tendon  fibers  at  their  ends 
and  these  fibers  may  continue  into  the  intramuscular  tissue,  or 
if  the  spindle  be  near  the  tendon  end  of  the  muscle  the  fibers  become 
continuous  with  those  of  the  tendon.  One  or  more  nerves  enter 
the  organ  near  its  equator  and  branch  just  inside  of  the  capsule; 
these  lose  their  sheaths  and  wind  about  the  intrafusal  fibers  in  the 


Fig.  115. — Pacinian  Body 
from  Mesentery  of  a 
Cat. 

1.  Fat  cells;  2,  artery;  3, 
nerve  fiber;  4,  inner  bulb; 
5,  axis  cylinder;  6,  layers 
of  the  capsule.  (Sldhr's 
Histology.) 


184 


PRACTICAL   HISTOLOGY 


form  of  rings  or  spirals  or  may  form  a  series  of  telodendrites.  These 
all  terminate  in  flower -spray  endings  upon  the  surface  of  the  various 
intrafusal  muscle  fibers.  Although  these  terminations  resemble 
motor  terminals  they  are  sensor.  Motor  terminals  have  been  dem- 
onstrated in  these  muscle  fibers. 

The  spindles  are  numerous  in  some  muscles  (small  muscles  of 
the  hands  and  feet),  few  in  others  (eye  muscles),  and  absent  in  others. 
They  measure  from  i  mm.  to  5  mm.  in  length  and  0.1  mm.  to 0.2  mm. 


3         ""Medullated  nerve  fiber. 


Terminal  ramification.     Tendon  bundle 


Fig.   116. — Texdon-spindle  of  a  Cat.     (Slohr's  Histology.) 

in  diameter.  Each  has  its  own  blood-vessels  that  accompany  the 
nerve  through  the  capsule. 

Tendon  spindles  resemble  muscle  spindles  except  that  the  intra- 
fusal fibers  are  tendon  fibers  and  the  naked  axones  do  not  wind 
around  the  intrafusal  fibers  but  branch  into  minute  fibers  that 
terminate  in  little  plates  upon  the  tendon  bundles.  They  are  most 
numerous  near  the  junction  of  the  muscles  and  tendons. 

The  motor  terminals  comprise  those  in  voluntary  striated  muscles, 
those  of  smooth  and  of  cardiac  muscle  tissues  and  those  of  glands. 

The  nerves  of  the  voluntary  striated  muscles  are  of  the  myelinated 
type  and  are  comparatively  large.  After  passing  through  the  epimy- 
sium  the  nerve  divides  into  branches  that  form  a  plexus  in  the  peri- 


NERVE   TISSUES 


185 


mysial  sheaths.  From  this  plexus  fibers  enter  the  fasciculi  and  form 
a  plexus  in  the  endoneurium.  As  such  a  nerve  does  not  contain  as 
many  fibers  as  there  are  muscle  fibers,  usually,  the  fibers  that  arc- 
derived  from  the  endomysial  plexus  give  off  branches  or  collaterals 
so  that  there  will  ultimately  be  as  many  nerve  fibers  as  there  are 


Fig.   117. — Motor  Nerve-endings  in  Intercostal  Muscle  of  a  Rabbit. 

a,   Sensor  nerve  fiber;  b,   muscle  fibers;  c,   motor  plates;  d,   myelinated  nerve 
fiber;  e,  bundle  of  nerve  fibers.      (Stohr's  Histology.) 


t.f-      >gf 


Iff  fjjIMW* 

B 

118. — Motor  Plates. 

A,  Surface  view,  from  a  guinea-pig.  B,  Vertical  section,  from  a  hedgehog. 
(After  Bohm  and  von  Davidoff).  g,  Granular  substance  of  the  motor  plate; 
m,  striated  muscle;  n,  nerve  fiber;  t.r.,  terminal  ramifications  of  the  nerve- 
fiber. 

muscle  fibers.  As  this  terminal  nerve  fiber  pierces  the  sarcolemmal 
sheath  the  neurolemma  and  myelin  sheath  blend  with  the  sarco- 
lemma  and  the  naked  axis  cylinder  alone  enters  the  muscle  fibers. 
This  passes  to  the  sole-plate  which  is  a  mass  of  granular,  nucleated 
protoplasm.     Within  this  the  fibrillar  of  the  nerve  fiber  terminate 


i86 


PRACTICAL  HISTOLOGY 


in  bulbous  enlargements,  which,  with  the  sole-plate  constitute  the 
end-plate.     There  is  but  one  organ  to  each  muscle  fiber. 

The  smooth  muscles  are  supplied  by  the  sympathetic  nerves. 
These  form  plexuses  between  the  fasciculi  or  muscle  layers  and  at 
the  intersections  of  the  meshes  ganglion  cells  are  to  be  found. 
Fibers  (amyelinated)  from  this  plexus  may  form  a  secondary  plexus 
in  between  the  muscle  fibers  and  from  this  the  terminal  fibers  pass 


Fig.   119. — Termination  of  Secretor  Nerve  Fibers  in  the  Tubules  of  the 
Submaxillary  Gland  of  a  Dog.     {After  G.  Retzius.) 

to  the  muscle  cells.  Here  they  end  as  tapered,  or  bulbous  extremities 
that  are  applied  to  the  surface  of  the  muscle  cells.  Some  of  the 
fibers  of  smooth  muscle  are  of  sensor  function. 

Cardiac  muscle  is  also  supplied  by  the  sympathetic  system.  The 
fibers  may  form  delicate  plexuses  at  the  intersections  of  which  are 
found  ganglia  of  various  sizes.  Individual  amyelinated  nerve  fibers 
pass  to  each  muscle  cell  and  terminate  upon  its  surface  in  many  fine 
fibrils  that  spread  over  each  nucleated  segment  or  cell.  Some  of 
the  fibrils  may  terminate  in  small  granules  or  knobs. 

In  secreting  glands  the  nerve  fibers  are  amyelinated  and  arise  in 
svmpathetic  ganglia.  In  the  gland  the  nerve  fibers  pass  to  the 
secreting  epithelium,  divide  into  fibrils  each  of  which  terminates  in 
a  varicose  manner  between  and  upon  the  cells  but  does  not  pass  into 
the  cells.     These  are  the  secretor  fibers. 


CHAPTER  VII 

CIRCULATORY  SYSTEM 

The  circulatory  system  comprises  the  heart,  arteries,  capillaries, 
veins  and  the  circulating  fluid,  the  blood. 

THE  HEART 

The  heart  is  the  most  important  member,  as  on  its  contractions 
depends  the  circulation.  It  is  a  thick-walled,  hollow,  muscular 
organ  composed  of  three  coats,  the  endocardium,  myocardium 
and  epicardium.  These  three  coats  are  analogous  to  the  coats  of 
the  vessels.  Of  these  three  the  one  that  continues  with  the  least 
change  throughout  the  vessels  is  the  internal  coat;  of  this  the 
endothelial  layer  continues  in  an  unbroken  line  through  the 
arteries,  capillaries  and  through  the  veins  back  to  the  heart.  The 
walls  of  the  chambers  have  not  all  the  same  thickness  and  this  is 
due  to  the  different  quantity  of  muscle  tissue  present.  The  reason 
for  this  difference  is  that  in  the  two  sets  of  chambers  the  muscular 
effort  required  of  them  is  not  the  same. 

The  endocardium  consists  of  a  lining  of  endothelial  cells  which  rest 
upon  the  subendothelial  (fibro-elastic)  tissue.  It  is  thicker  in  the 
atria  than  in  the  ventriculi.  Although  the  endocardium  is  smooth, 
glistening  and  transparent  it  does  not  always  run  an  even  and  smooth 
course  as  in  the  blood-vessels  as  in  parts  of  the  chambers  the  myo- 
cardium is  very  irregulary  arranged.  The  endocardium  lines  every 
part  of  these  chambers,  covers  the  valves  and  chordae  tendineae 
and  is  continuous  with  the  intima  of  the  vessels  of  the  heart. 

The  endothelial  cells  are  flattened,  nucleated  plates  that  have 
an  irregular  outline  and  are  held  together  by  a  small  amount  of  in- 
tercellular cement.  They  differ  but  slightly  from  those  found  within 
the  vessels.  The  layer  of  cytoplasm  may  be  so  thin  that  the  nuclei 
project  somewhat. 

187 


1 88  PRACTICAL   HISTOLOGY 

The  subendothelial  tissue  consists  of  delicate  fibroelastic  tissue. 
The  outer  part  of  this  layer  (next  to  the  myocardium)  contains  less 
elastic  tissue  and  the  fibers  are  usually  coarse.  Frequently  fat  is 
found  here.  It  may  contain  a  few  involuntary  nonstriated  muscle 
fibers.  Here  also  are  seen  some  partly  developed  heart  muscle  fibers, 
called  Purkinjc  fibers;  the  fibrillar  are  few  and  form  a  peripheral  ring 
in  these  muscle  fibers.  They  are  common  in  some  mammalian 
hearts,  and  in  man  they  are  represented  by  the  terminals  of  the 
Bundle  of  His. 

Over  the  chordae  tendineae  and  papillary  muscles  the  endocar- 
dium is  very  thin  and  the  elastic  tissue  is  less  in  amount. 

Guarding  the  atrioventricular  orifices  and  the  openings  into  the 
pulmonary  artery  and  aorta  are  duplications  of  the  endocardium 
called  valves.  Around  the  openings  the  fibroelastic  tissue  is  con- 
densed to  form  a  ring-like  mass,  the  annuli  fibrosi.  These  rings 
serve  as  origins  for  the  valves  and  muscle.  In  the  larger  quad- 
rupeds cartilage  may  be  present. 

The  atrioventricular  valves  consist  of  two  layers  of  endocardium 
continuous  at  the  free  edges  of  the  valves;  the  central  part  consists 
of  a  layer  of  tough  white  fibrous  tissue  containing  but  few  elastic 
fibers.  This  central  tissue  is  continuous  with  the  rings  and  the 
chordae  tendineae.  At  the  bases  of  the  valves  there  is  a  considerable 
quantity  of  smooth  muscle  tissue  which  may  act  as  a  constrictor  of 
the  orifice.  The  atrial  muscle  may  extend  for  a  short  distance 
into  the  atrioventricular  valves. 

The  chordce  tendineae  consist  of  cords  of  white  fibrous  tissue 
surrounded  by  a  thin  layer  of  the  endocardium.  Above  they- are 
attached  to  the  valves  where  the  endothelial  surface  becomes  con- 
tinuous with  that  of  the  valve  and  the  central  cord  fibers  pass  to  the 
central  fibrous  mass  of  the  valve  and  join  it  in  a  radiating  manner. 
Below  they  are  attached  to  the  papillary  muscles  where  the  endothe- 
lial surfaces  are  continuous  and  the  central  fibers  blend  with  the 
endomysium  of  the  papillary  muscles. 

The  semilunar  valves  have  the  same  general  structure.  They 
differ  in  several  ways.  No  chordae  tendineae  are  present  and  each 
valve  possesses  a  marginal  band,  under  the  endocardium,  in  the 
middle  of  which  there  is  an  enlargement,  the  corpus  Arantii.     At 


CIRCULATORY    SYS  I  I :  \1 


189 


each  side  of  the  corpus  there  is  a  small  semilunar  fold  called  the 
lunula.  The  band  strengthens  the  free  edge  of  the  valve  while  the 
nodule  probably  ensures  complete  closure  of  the  valves.  These 
valves  are  thinner  than  the  atrioventricular  valves.  The  atrial  myo- 
cardium may  continue  into  their  bases.  Blood-vessels  extend  into 
them  as  far  as  the  muscle  tissue  penetrates.  The  aortic  valves  are 
more  elastic  on  the  ventricular  surface  than  upon  the  aortic  surface. 


Fig.  120. — Section  of  the  Root  of  the  Aorta  and  an  Aortic  Valve. 
a,   Aorta;  b,   aortic  valve,   c,   sinus  of  Valsalva.      (Photograph.     Obj.  32  mm, 

5X0 


oc. 


The  atrioventricular  bundle,  or  bundle  of  His,  consists  of  a  bundle 
of  peculiar  fibers  that  connects  atria  and  ventricles.  It  arises  in  the 
interatrial  septum  and  on  the  right  side  thereof,  near  the  orifice  of  the 
coronary  sinus,  and  adjacent  points;  it  then  passes  forward  between 
the  annulus  ovalis  and  the  atrioventricular  orifice,  the  fibers  converg- 
ing to  form  a  node;  from  this  node  a  single  bundle  is  formed  that 
turns  down  into  the  atrioventricular  septum  at  the  base  of  the 
median  leaflet  of  the  tricuspid  valve;  it  passes  into  the  pars  mem- 


190  PRACTICAL  HISTOLOGY 

branacea  sepli,  and  at  the  beginning  of  the  muscular  portion  of  the 
interventricular  septum  it  divides  into  two  fasciculi,  one  for  each 
ventricle.  These  bundles  lie  just  beneath  the  endocardium,  sur- 
rounded and  insulated  by  fibrous  connective-tissue  sheaths.  Pass- 
ing toward  the  apex  of  the  heart  each  bundle  upon  reaching  the 
lower  third  sends  branches  to  the  papillary  muscles  and  there  forms 
a  large  number  of  twigs  that  extend  in  all  directions  over  the  ven- 
tricular surface  and  come  into  histologic  relation  with  the  cardiac 
muscle  fibers.  The  main  bundle  is  in  relation  with  a  bursa  and  the 
entire  bundle  is  supplied  by  an  artery  from  the  right  coronary. 
Other  similar  fibers  form  a  network  in  the  atrial  wall  near  the 
entrance  of  the  superior  vena  cava.  These  constitute  the  node  of 
Keath  and  Flack.     Here  the  cardiac  contraction  begins. 

The  muscle  fibers,  less  differentiated  than  those  of  the  general 
myocardium  are  striated  but  the  sarcoplasm  predominates.  The 
fibrillar  are  few  and  peripherally  placed,  forming  a  circle,  or  irregular 
or  triangular  groups.  The  volume  and  size  is  greater  than  in  the 
ordinary  cardiac  fibers.  The  pigmentation  is  localized  and  not 
prominent.  The  cell-boundaries  cannot  be  definitely  located  so 
that  these  cells  form  a  syncytium.  These  fibers  represent  early 
stages  of  muscle  development  from  undifferentiated  protoplasm. 
The  vagal  and  sympathetic  nerves  supply  this  bundle. 

The  myocardium  consists  of  involuntary  striated  muscle.  In  the 
atria  the  fibers  are  arranged  in  two  layers,  inner  and  outer.  The 
inner  layer  consists  of  two  sets,  one  of  which  loops  over  each  atrium 
from  front  to  back;  the  other,  annular  fibers  surround  the  append- 
ages and  form  rings  about  the  orifices  of  the  veins  and  the  fossa 
ovalis.  In  the  outer  layer  the  fibers  run  transversely  from  one 
atrium  to  the  other  predominating  upon  the  ventral  surfaces  of  the 
atria.  In  the  ventricles  the  fibers  cannot  be  separated  so  dis- 
tinctly into  layers.  Some  run  longitudinally,  others  transversely, 
while  the  greatest  number  have  an  oblique,  circular,  or  spiral  course, 
forming  even  a  figure  eight.  Owing  to  this  arrangement  distinct 
lamellae  cannot  be  formed.  Usually  incomplete  internal  and  external 
longitudinal  layers  are  formed  between  which  are  seen  the  circular 
fibers  that  form  the  thickest  layer.  Besides  the  latter  are  found 
spiral  and  oblique  fibers  that  are  present  chiefly  in  the  upper  and 


CIRCULATORY    SYSTEM!  igi 

lower  portions  of  the  left  ventricle.     Most  of  the  layers  terminate 
in  the  papillary  muscles. 

A  delicate  meshwork  of  areolar  tissue  is  seen  between  the  muscle 
libers;  this  is  the  cndomysium  and  it  supports  the  numerous  vessels 
and  muscle  libers.  At  the  endocardial  and  epicardial  surfaces  of  the 
myocardium  the  fibrous  tissue  is  a  little  more  abundant  and  serves 
to  connect  these  coats  together.  These  layers  of  fibrous  tissue 
constitute  the  internal  and  external  perimysial  sheaths,  respectively. 

The  epicardium,  or  visceral  layer  of  the  pericardium,  consists  of  a 
single  layer  of  endothelial  cells  resting  upon  the  sub  endothelial  tissue. 
It  differs  from  the  endocardium  in  possessing  no  muscle  tissue  and  is 
separated  from  the  myocardium  more  or  less  completely  by  a  thin 
layer  of  adipose  tissue.  The  deeper  fibers  connect  it  with  the  ex- 
ternal perimysium  of  the  myocardium.  It  is  thickest  over  the  main 
branches  of  the  coronary  vessels  where  fat  is  usually  found. 

The  pericardium  consists  of  two  parts,  serous  and  fibrous.  The 
serous  pericardium  is  a  continuation  of  the  epicardium  over  the  great 
vessels  and  upon  the  inner  surface  of  the  fibrous  portion.  The  fibrous 
portion  is  a  sack-like  organ,  consists  of  dense  white  fibrous  tissue 
and  serves  as  a  protection  to  the  heart.  It  is  attached  by  its  base  to 
the  diaphragm  and  its  apex  is  continuous  with  the  fascia  of  the  neck. 

The  blood-vessels  of  the  heart  are  branches  of  the  coronary 
arteries;  the  capillaries  form  plexuses  parallel  to  the  long  axes  of 
the  muscle  strands  and  they  may  even  lie  in  grooves  on  the  strands. 
The  venous  capillaries  attain  a  size  of  0.25  mm.  before  continuing 
as  venules.  The  endocardium  is  nourished  by  the  blood  that  flows 
over  it. 

The  lymphatics  are  superficial  and  deep.  They  are  present  in  all 
of  the  coats  but  do  not  communicate  with  one  another  to  any  great 
extent.  The  lymph  capillaries  are  numerous  especially  in  the 
myocardium  and  epicardium. 

The  nerves  are  from  both  systems  and  sympathetic  ganglia  are 
numerous.  The  sensor  nerve  plexuses  are  subendocardial.  The 
fibers  end  in  direct  contact  with  the  endothelial  cells  of  the 
endocardium  and  chordae  tendineae.  In  addition  end-plates  are 
also  present,  especially  in  the  atrial  endocardium  and  in  the 
epicardium. 


192  PRACTICAL   HISTOLOGY 

The  afferent  nerves  are  derived  from  plexuses  at  the  intersection 
of  which  are  found  ganglia  of  various  sizes.  Individual  amyelinated 
nerve  fibers  pass  to  each  muscle  cell  and  terminate  upon  its  surface 
in  many  fine  fibrils  that  spread  over  each  nucleated  segment  or  cell. 
Some  of  the  fibrils  may  terminate  in  small  granules  or  knobs.  The 
ganglia  comprise  four  to  five  groups  of  ganglion  cells  upon  the  dorsal 
walls  of  the  atria  in  the  region  of  the  interatrial  septum. 

The  blood  is  sent  from  and  returned  to  the  heart  by  the  vessels. 
Of  these  there  are  three  varieties:  (1)  arteries,  or  efferent  vessels; 
(2)  capillaries,  or  connecting  vessels;  (3)  veins,  or  afferent  vessels. 

The  arteries  carry  oxygenated  blood  with  the  exception  of  the 
pulmonary  arteries;  the  latter  in  that  one  particular  resemble  veins. 
Arteries,  however,  always  carry  the  blood  away  from  the  heart, 
toward  the  periphery. 

1.  For  convenience  of  description,  the  arteries  or  efferent  vessels 
are  classed  as  large,  medium  and  small.  The  large  are  the  aorta 
and  pulmonary  artery;  the  medium  the  remainder  of  the  named 
arteries  of  the  body,  and  the  small,  the  unnamed  branches  that 
gradually  become  capillaries.  All  have  the  same  general  structure, 
consisting  of  three  coats,  tunica  intima,  tunica  media  and  tunica 
adventitia ;  they  carry  the  blood  from  the  heart. 

As  the  medium-sized  artery  is  the  type,  its  description  will  be 
considered  first  and  then  the  differences  between  it  and  the  others 
will  be  pointed  out. 

Medium-sized  Artery. — The  tunica  intima,  or  interna,  consists 
of  three  layers,  the  endothelial,  sub  endothelial  and  an  internal  elastic 
lamina.  It  is  elastic  but  easily  broken  in  any  direction  so  that  it 
does  not  strip  readily.  It  is  usually  corrugated  or  wrinkled  due  to 
the  contraction  of  the  artery  after  death. 

The  endothelial  cells  are  elliptical,  or  irregular,  elongated  cells  with 
clear  outlines  and  prominent  nucleus  and  nucleolus.  The  layer  of 
cytoplasm  is  usually  so  thin  that  the  nuclei  form  a  bulge.  The  cells 
form  a  continuous  surface  and  their  serrated  edges  are  held  together 
by  a  small  amount  of  intercellular  cement.  This  is  readily  outlined 
by  the  silver  nitrate  method.  These  cells  rest  upon  the  subendothe- 
lial  fibroelastic  tissue  in  which  numerous  tissue  spaces  exist.  The 
elastic  fibers  are  delicate  and  this  layer  is  usually  thin. 


CIRCULATORY   SYSTEM 


193 


Limiting  this  coat  is  a  prominent  wavy  band  (on  transverse  section 
of  the  artery)  of  elastic  tissue,  the  internal  elastic  lamina.  This  is 
usually  not  solid  but  shows  a  number  of  perforations  for  which  reason 
it  is  sometimes  called  a,  fenestrated  membrane.  It  does  not  take  the 
ordinary  plasmatic  stains  well  and  therefore  appears  as  a  light  band. 
It  stains  readily  with  the  elastica  stains. 


Fig.  121. — Cross-section  of  a  Medium-sized  Artery. 
a,  Intima;  b,  media;  c,  adventitial  d,  endothelial  cells;  e,  subendothelial  tissue; 
/,  internal  elastic  lamina;  g,  circular  muscle  tissue;  h,  elastic  fibers;  i,  ex- 
ternal elastic  lamina;  k,  white  fibrous  tissue;  I,  arteriole;  m,  venule,  vasa 
vasorum. 

The  tunica  media  consists  chiefly  of  circularly  arranged  involun- 
tary nonstriated  muscle  tissue.  The  fibers  are  small  and  closely 
packed.  At  the  origins  of  the  branches  of  the  abdominal  aorta 
oblique  and  even  longitudinally  arranged  smooth  muscle  may  be 
found.     The  muscle  fibers  are  held  together  by  a  small  amount  of 

13 


194 


PRACTICAL  HISTOLOGY 


white  fibrous  tissue  and  numerous  yellow  elastic  fibers  are  present. 
Some  of  the  latter  run  transversely  and  others  course  obliquely. 
Often  a  band  of  elastic  tissue  separates  the  media  from  the  ad- 
ventitia;  this  is  the  external  elastic  lamina  but  it  is  not  so  thick  nor 
so  prominent  as  the  internal  lamina.  Some  consider  this  lamina 
a  part  of  the  adventitia. 


Adventitia 


Fig.   12  2.- — Cross-section  of  the  Human  Aorta.     Hematoxylin  and  Eosin 
Stain.      (Photograph.     Obj.  16  mm.,  oc.  7.5  x.) 

The  media  forms  a  considerable  portion  of  the  thickness  of  the 
arterial  wall  and  it  is  usually  thicker  on  one  side  than  the  other. 

The  tun  ca  adventitia,  or  externa,  is  a  thick  fibro-elastic  coat, 
and  protects  the  vessel  from  undue  dilatation.  The  elastic  tissue 
is  very  abundant  and  consists  of  coarse  fibers  that  are  longitudinally 


CIRCULATORY   SYSTEM 


195 


arranged  near  the  media.  In  some  vessels,  as  renal  and  splenic 
arteries,  longitudinal  muscles  fibers  are  found.  It  is  about  one-half 
or  two-thirds  the  thickness  of  the  media.  This  coat  contains  the 
larger  trunks  that  nourish  the  vessels,  the  vasa  vasorum.  The  nervi 
vasorum  are  present  also,  and  form  branches  that  pass  to  the 
muscle  coat. 


Intimia 


Media  — 


Adventitia 


Fig.   123. — Cross-section    of    the    Human    Aorta.     Weigert's    Elastica 
Stain.     (Photograph.     Obj.  16  mm.,  oc.  5  X.) 


The  large  arteries  are  mainly  elastic  tubes.  The  intima  is  not  so 
distinct  and  gradually  fades  into  the  media.  The  endothelial  cells 
are  shorter.  In  the  aorta  an  internal  elastic  lamina  is  not  present 
but  is  often  found  in  the  common  iliac  arteries  where  it  may  be 
double.  The  elastic  fibers  usually  fuse  to  form  the  fenestrated 
membrane  of  Henle.  Although  the  media  is  very  thick  the  muscle 
tissue  is  comparatively  scant  and  the  elastic  tissue  predominates. 
The  muscle  fibers,  which  are  often  forked,  are  scattered  among  the 


196  PRACTICAL   HISTOLOGY 

elastic  fibers  so  that  this  coat  does  not  stain  as  deeply  as  the  corre- 
sponding coat  of  the  medium-sized  arteries.  This  coat  is  very  elastic 
but  not  contractile.  The  same  structure  prevails  in  the  large  branches 
of  the  aorta.  The  adventitia  is  usually  thin  but  otherwise  resembles 
that  of  other  arteries. 

In  small  arteries  the  muscle  tissue  predominates  and  these  are 
contractile  tubes.  The  intima  is  thinner  but  the  elastic  lamina  is 
very  prominent  and  thick.  The  media  is  proportionately  thicker 
than  in  other  arteries  and  consists  entirely  of  smooth  muscle-tissue 
circularly  arranged.  Elastic  tissue  is  practically  absent  although  at 
times  a  thin  external  elastic  lamina  may  be  seen.  The  adventitia 
is  thin. 

From  birth  to  old  age  the  intima  increases  rapidly  from  6  microns 
to  19  microns  in  thickness  and  the  media  up  to  650  microns,  while 
the  adventitia  decreases.  *  As  old  age  advances  the  vessels  lose  their 
elasticity  through  the  conversion  of  the  elastic  tissue  into  inelastic 
elacin.  As  the  continued  blood-pressure  would  tend  to  increase  the 
caliber  this  condition  is  overcome  by  the  special  thickening  of  the 
intima. 

The  difference  in  structure  may  be  explained  by  the  difference  in 
function  of  the  arteries.  The  large  arteries  are  practically  elastic 
tubes,  the  main  tissue  being  elastic.  These  vessels  must  be  able  to 
suddenly  increase  their  capacity  and  return  to  the  normal  caliber 
without  injury  but  they  must  not  reduce  their  caliber  to  any  appre- 
ciable extent.  When  the  heart  contracts  a  large  volume  of  blood  is 
suddenly  forced  into  the  large  arteries  and  they  dilate  to  accommodate 
it.  Through  the  natural  recoil  of  the  stretched  elastic  tissue  and  the 
removal  of  the  resistance  ahead  (the  flow  of  the  blood  into  the  smaller 
arteries)  the  blood  in  the  large  arteries  is  gradually  forced  onward  and 
the  vessels  return  to  their  normal  caliber.  They  must  not  decrease 
this  caliber  for  if  that  were  to  occur  it  would  increase  the  resistance 
to  the  blood  entering  from  the  heart  and  cause  this  organ  to  hyper- 
trophy to  overcome  this  increased  resistance. 

The  medium-sized  arteries  are  mainly  contractile  vessels  and  yet 
they  have  sufficient  elastic  tissue  in  their  walls  to  permit  of  some 
dilatation.  Their  normal  caliber  is  sufficient  for  the  ordinary  blood- 
supply  and  if  more  blood  is  required  they  can  relax  their  muscle 


CIRCULATORS    SYS1  l  \1 


197 


tissue  and  even  be  stretched  some  without  injury.  If  the  amount  of 
blood  be  too  great  these  vessels  can  contract  and  cut  down  the 
amount  somewhat. 

The  small  arteries  and  arterioles  have  no  elastic  tissue  except  an 
elastic  lamina.  These  vessels  are  the  ones  that  mainly  control  the 
supply  of  blood  to  a  part  and  it  is  upon  these  that  many  drugs  given 
for  that  action  have  their  effect.  These  are  essentially  only  contractile 
tubes  and  are  for  the  purpose  of  cutting  down  the  amount  of  blood  and 
to  prevent  congestion.     If  that  amount  is  not  sufficient  then  by  the 


Fie.  124. — Small  Arteriole  Forming  Capillaries. 

The  irregular  outlines  of  the  endothelial  cells  are  shown.     (From  Schafer  after 

Mann.) 


relaxation  of  the  muscle  tissue  in  their  walls  the  vessel  increases  its 
caliber  and  so  permits  of  more  blood.  The  caliber  of  these  vessels 
in  the  living  condition  is  somewhat  smaller  than  in  the  dead  because 
under  normal  conditions  all  of  the  smooth  muscles  of  the  body  are 
slightly  contracted  all  of  the  time  and  this  is  called  tonic  contraction 
(due  to  adrenalin  probably).  If  this  tonic  contraction  be  withdrawn 
then  the  vessels  dilate  somewhat  through  the  relaxation  of  the 
muscle. 


198  practical  histology 

Variations  in  the  structure  of  some  of  the  arteries  are  to  be  found. 
The  roots  of  the  aorta  and  pulmonary  artery  usually  contain  a 
considerable  amount  of  cardiac  muscle  tissue.  The  arch  of  the  aorta 
may  contain  some  smooth  muscle  tissue,  longitudinally  arranged, 
in  all  three  coats.  Some  of  the  larger  branches  may  have  spirally 
directed  muscles,  especially  those  vessels  that  are  bent.  The  arteries 
of  the  brain  and  its  coverings  are  all  thin-walled  and  the  only  elastic 
tissue  present  is  in  the  lamina. 

As  the  vessels  become  reduced,  the  intima  is  the  first  to  suffer; 
the  subendothelial  tissue  disappears,  and  the  endothelial  cells  are 
seen  to  rest  upon  the  elastic  lamina.  The  media  becomes  atten- 
uated so  that  only  a  single  layer  of  muscle  fibers  is  seen.     This  soon 


Fig.   125. — Capillary  (Frog's  Mesentery)  Treated  with  Silver  Nitrate  to 
Outline  the  Endothelial  Cells.     (After  Ranvier.) 


becomes  reduced  to  a  few  stray  fibers.  The  adventitia  becomes 
greatly  reduced  and  is  represented  by  a  few  bundles  of  fibrous  tissue. 
This  is  practically  the  precapillary  vessel.  It  is  succeeded  by  the 
capillary. 

2.  The  capillaries  or  connecting  vessels  are  merely  delicate  tubes 
consisting  of  a  single  layer  of  endothelial  cells  placed  end  to  end, 
and  held  together  by  intercellular  cement.  These  are  readily  out-, 
lined  with  silver  nitrate.  These  cells  are  not  so  firmly  united  but 
that  the  leukocytes  can  force  their  way  between  them  (diapedesis) . 
These  openings  thus  formed  are  the  stigmata  and  they  are  not 
permanent.  The  endothelium  is  held  by  some  to  be  phagocytic. 
They  are  the  smallest  vessels,  and  anastomose  freely  to  form  loose 
or  dense  plexuses.  At  times  they  are  very  irregular,  possessing 
dilatations.  They  are  practically  very  thin  animal  membranes, 
and  through  their  walls  the  liquid  portion  of  the  blood  and  the 
ameboid  white  blood  cells  have  no  difficulty  in  passing  into  the 
surrounding  tissues.     Small  capillaries  average  5  to  7  microns  in 


CIRCULATORY   SYSTEM 


199 


diameter,  500  microns  in  length,  and  cross-sections  show  that  they 
are  encircled  by  two  endothelial  cells.  Large  capillaries  average 
8  to  13  microns  and  are  encircled  by  three  to  four  endothelial  cells. 
Stohr  claims  that  capillaries  can  contract  as  nerve  endings  are 
found  in  the  cells. 

Capillaries  are  found  in  practically  all  tissues  except  epithelium 
and  cartilage.     In  the  organs  in  general  the  capillaries  are  not  in 


Fig.  126, — Longitudinal  Section  of  Voluntary  Muscle  of  a  Guinea-pig, 

Injected,  Showing  the  Course  of  the  Capillaries. 

a,  Ampullae.     (Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 


direct  contact  with  the  functionating  cells  but  are  separated  by 
a  space  into  which  the  lymph  passes  and  bathes  the  cells.  The 
meshes  are  long  and  narrow  in  tendons,  muscles  and  nerves.  In 
mucous  membranes  and  the  skin  the  capillaries  form  loops.  In  the 
lungs,  glands  and  fat  the  meshes  are  close. 

In  certain  tissues  and  organs  the  capillaries  are  peculiarly  modified. 
In  the  skeletal  muscles  the  capillaries  run  parallel  to  the 
course  of  the  fibers  and  are  connected  to  one  another  by  cross- 


200 


PRACTICAL   HISTOLOGY 


branches  that  dilate  readily.  These  are  the  ampulla  and  during 
the  contraction  of  the  muscle  are  dilated  with  blood  from  the 
longitudinal  vessels,  and  so  take  the  strain  from  these.  In  the  liver, 
adrenal,  spleen  and  carotid  gland  the  endothelium  of  the  capillaries 
is  in  direct  contact  with  the  functionating  epithelium  or  parenchyma 
of  the  gland.  These  capillaries  are  called  sinusoids  (Minot)  and 
the  nutritional  relation  is  of  the  closest.  No  spaces  exist  between 
the  vessels  and  the  epithelium  and  the  nutritional  elements  pass 
directly  into  the  cells  and  any  internal  secretion  may  pass  directly 
into  the  capillaries.  In  parts  of  the  cortex  of  the  kidney  arterioles 
break  up  into  a  series  of  capillary  tufts  from  which  the  blood  is  again 
collected  by  the  efferent  arteriole;  the  tuft  is  a  series  of  capillaries. 


kc. 


Fig.  127. — Sinusoids  (Si)  in  the  Liver  of  a  Chick  Embryo  of  Eleven  Days. 

(Lewis  and  Stohr  after  Minot.) 
h.c,  Cords  and  tubules  of  hepatic  cells. 

interposed  between  two  arterioles  and  is  called  a  relia  mirabilia. 
In  the  penis  and  clitoris  no  regular  capillaries  exist  in  the  corpora 
cavernosa.  Here  the  arterioles  pass  the  blood  into  large  dilated 
cavernous  spaces  lined  with  endothelial  cells  and  these  are  sinuses. 
In  exposed  regions,  nose,  ears,  toes,  kidneys  and  membranes  of  the 
nerve  system,  direct  communications  between  the  arteries  and  veins 
exist.  These  are  anastomoses  and  are  not  to  be  confused  with  the 
anastomoses  that  normally  occur  between  arteries  which  form  the 
anastomotic  circulations  of  the  extremities  and  certain  organs. 


CIRCULATORY    SYSTEM  201 

The  veins  or  afferent  vessels  have  the  same  general  structure 
as  arteries  but  the  coats  are  thinner.  These  vessels  collapse  readily 
when  cut  but  they  are  nevertheless  strong.  They  carry  the  blood 
toward  the  heart,  are  more  numerous  and  larger  than  the  arteries 
and  anastomose  more  freely.  The  precapillary  venules  are  mere 
tubes  of  endothelium  supported  by  a  delicate  network  of  fibro- 
elastic  tissue. 

The  coats  are  tunica  intima,  tunica  media  and  tunica  adventitia. 

The  tunica  intima  is  usually  tougher  than  in  the  arteries  and  may 
be  stripped  more  readily.     The  endothelial  cells  are  short  and  broad; 


d 
Fig.  128. — Portion  of  a  Cross-section  of  a  Human  Vein. 
A,    Intima;   B,    Media;   C,   Adventitia — a,    Internal   elastic  lamina;  b,    smooth 
muscle  fibers;  c,  white  fibrous  connective  tissue;  d,   smooth  muscle  fibers 
in  the  adventitia.     (Stohr's  Histology.) 


the  subendothelial  tissue  is  not  well  developed  and  the  internal 
elastic  lamina  is  not  marked  as  the  elastic  tissue  tends  to  form  a 
sort  of  network  and  not  a  membrane.  In  some  veins  smooth 
muscle  tissue  longitudinally  arranged  is  found  in  the  intima. 

At  intervals  this  coat  is  thrown  into  folds  called  valves.  These 
are  duplications  of  the  intima.  Each  valve  is  a  semilunar  fold  of 
intima  having  a  central  mass  of  white  fibrous  tissue  that  gives  it 
added  strength.  These  are  usually  attached  in  pairs  and  opposite 
the  points  of  attachment  the  vein  is  dilated  forming  pouches  or 


202  PRACTICAL  HISTOLOGY 

sinuses.  When  filled  with  blood  these  pouches  produce  a  marked 
bulge.  The  valves  prevent  a  reflux  of  the  blood  but  present  no 
obstruction  to  the  onnowing  blood.  Valves  occur  in  all  of  the 
veins  except  the  venae  cavae,  portal,  pulmonary,  hepatic,  innominate, 
common  iliacs,  mesenteric,  splenic,  uterine,  ovarian,  cranial  cavity, 
vertebral  canal,  cancellous  bone  and  the  renal  veins. 

The  tunica  media  contains  a  relatively  small  amount  of  smooth 
muscle  tissue  that  is  circularly  arranged.  The  bulk  of  this  coat 
consists  of  fibroelastic  tissue.  In  the  veins  of  brain  and  bones  and 
in  the  thoracic  part  of  the  inferior  vena  cava  muscle  tissue  is  wanting. 
In  the  crural,  mesenteric  and  iliac  veins  some  longitudinal  muscle 
tissue  is  found  near  the  intima. 

The  tunica  adventitia  is  the  most  prominent  coat.  In  some  vessels 
as  the  abdominal  part  of  the  inferior  vena  cava,  renal,  spermatic, 
azygos,  external  iliac,  splenic,  hepatic  and  portal  veins  longitudinal 
smooth  muscle  tissue  may  be  found  in  it.  It  consists  of  coarse 
bundles  of  white  fibrous  and  yellow  elastic  tissues  and  contains 
the  vessels  and  nerves  of  the  vein. 

Veins  are  merely  conducting  vessels  and  cannot  assist  in  forcing 
the  blood  along  as  arteries  do.  They  must  be  capable  of  considerable 
distention  and  no  contraction,  hence  the  presence  of  fibro-elastic 
tissue  in  preponderance  in  the  media  and  the  small  quantity  of 
muscle  tissue. 

The  blood-vessels  are  nourished  by  the  vasa  vasorum.  These  He 
in  the  adventitia  and  from  them  small  branches  pass  chiefly  to  the 
media,  mainly  for  the  muscle  tissue.  The  intima  has  very  few 
capillaries  as  it  is  nourished  by  the  blood  that  flows  over  it. 

Lymphatics  are  numerous.  Blood-vessels  are  often  the  centers  of 
extensive  lymph  channels  that  lie  in  the  adventitia,  and  constitute 
the  perivascular  lymphatics. 

The  nerves  are  chiefly  sympathetic  and  are  distributed  to  the 
media  and  adventitia.  These  are  the  nervi  vasorum  and  they  form 
plexuses  around  the  vessels.  They  are  motor  and  sensor.  The 
motor  fibers  utimately  terminate  in  the  muscle  tissue.  The  sensor 
libers  are  connected  with  end-plates  in  the  intima.  Pacinian  bodies 
are  also  found  in  the  adventitia. 


CIRCULATORY  SYSTEM 
Table  of  Comparison  of  Arteries  and  Veins 


203 


Character 

Arteries 

Veins 

Coats. 

Three. 

Three. 

Size. 

Thick. 

Thin. 

Intima. 

Elastic 
nent. 

lamina         prorni- 

Not  prominent;  may  be 
absent. 

Media. 

Mainly 

smooth     muscle. 

Little  muscle,  mainly  white 
fibrous  tissue. 

When  empty. 

Do  not  ( 

:ollapse  readily. 

Collapse  readily. 

Valves. 

Absent. 

Usually  present. 

Course      of 

the 

blood. 

From  the  heart. 

Toward  the  heart. 

Character    of 

the 

Oxygenated   (with  exception 

Deoxygenated    (with   excep- 

blood. 

of  that 
artery). 

in  the  pulmonary 

tion  of  that  in  the  pulmonary 
veins). 

BLOOD 

Blood  and  lymph  are  the  only  liquid  connective  tissues.  Blood  is 
of  an  alkaline  reaction,  has  a  peculiar  and  characteristic  odor  due 
to  a  volatile  fatty  acid  in  combination,  with  an  alkaline  base.  Its 
specific  gravity  (1.051  to  1.056)  is  diminished  by  liquid  foods  and 
increased  by  solid  foods.  The  temperature  averages  38°C.  This 
varies  as  follows:  Inferior  vena  cava  36.7°C.  (q8.2°F.);  hepatic  vein 
39.7°C.  (103. 4°F.).  It  is  composed  of  cellular  elements,  the  cor- 
puscles, and  the  intercellular  substance,  or  liquor  sanguinis.  The 
quantity  of  blood  seems  to  vary  at  different  ages.  In  the  infant 
it  represents  one-nineteenth  of  the  body  weight  and  in  the  adult 
one-thirteenth,  although  later  investigation  seems  to  give  one-nine- 
teenth also  for  the  adult. 

The  cellular  elements  are  of  three  varieties,  the  red  cells,  white 
cells  and  platelets.  These  are  said  to  represent  328  parts  and  the 
liquor  sanguinis  672  parts. 

The  red  cells,  or  erythrocytes,  are  nonnucleated,  bell-shaped  ele- 
ments varying  from  5  to  9  microns  and  averaging  7  to  8.5  microns 
in  diameter  and  1.9  to  2.0  microns  in  thickness.  The  bell-shape  is 
not  seen  unless  the  necessary  precautions  are  exercised,  that  is  to 


204 


PRACTICAL   HISTOLOGY 


fix  the  blood  before  it  becomes  exposed  to  the  air  (see  Blood  Technic, 
p.  44).  These  cells  have  been  studied  under  various  conditions 
by  Weidenreich  and  Lewis  and  the  author  has  found  that  they  are 
to  be  readily  studied  in  fetal  tissues.  Upon  exposure  to  air  these 
bell-shaped  cells  collapse  and  this  accounts  for  the  usual  description 
as  that  of  a  biconcave  disc.  Schafer  and  others  maintain  that  the 
red  cells  are  normally  biconcave.  When  fresh  normal  blood  is 
examined  under  the  microscope  these  cells  form  rouleaux,  and  this 
is  said  to  be  due  to  the  cells  fitting  into  one  another.  When  exposed 
to  air  these  cells  collapse  and  resemble  rolls  of  coins  on  edge. 


\ 


X 


Fig.   129. — Red  Blood  Cells. 
Red    blood-cells,      i,    Bell-shaped    red    blood-cell  of  man;    2,    surface    view  of 
collapsed  bell-shaped  cell;  3,  side  view  of  2;  4,  surface  view  of  red  blood  cell 
of  the  frog. 


Under  the  microscope  each  cell  is  pale  straw-colored  or  greenish. 
It  consists  of  a  framework,  the  stroma,  that  contains  an  organic 
iron  compound  that  carries  the  oxygen;  this  is  the  hemoglobin.  The 
presence  of  a  cell  membrane  is  still  a  matter  of  dispute. 

Weidenreich  states  that  the  red  cells  are  surrounded  by  a  struc- 
tureless and  colorless  membrane  enclosing  a  colored  semi-fluid  mass 
that  consists  chemically  of  proteins,  lecithin,  cholesterin,  inorganic 
salts  and  hemoglobin.  A  stroma  does  not  exist  in  the  adult  stage 
of  the  cells.  The  envelop  will  stain  with  magenta  and  methyl 
violet.  It  is  elastic  and  the  cells  can  change  their  form  and  regain 
their  shape. 

Some  cells  average  from  5.5  to  7.5  microns,  and  are  called  mi- 
eroeytes,  while  those  over  8.5  microns  are  maeroeytes.  Bethe  found  the 
various  red  cells  in  the  following  proportions:  6.92  microns,  42  per 


CIRCULAH  >RY    SYS1  :  20j5 

cent.;  7.26  microns,  28  per  cent.;  8.58  microns,  16  per  cent.;  6.6 
microns,  8  per  cent.;  9.24  microns,  6  per  cent. 

In  normal  blood,  the  cells  tend  to  form  rolls,  or  rouleaux.  Under 
the  same  condition,  5,000,000  corpuscles  are  found,  per  cubic  mm., 
in  the  male,  and  about  4,500,000  in  the  female. 

Nucleated  red  blood-cells,  or  erythroblasts  are  found  in  the  fetus, 
in  red  bone-marrow  and  in  the  spleen  (at  times; .  The  cells  of 
average  size  are  called  normoblasts,  the  smaller  ones  microblasts  and 
the  larger  ones  macroblasts. 

In  fishes,  amphibians,  reptiles  and  birds  the  red  cells  are  nucleated 
and  usually  oval  in  form.  In  mammals  they  are  nonnucleated  and 
circular  in  form,  with  the  exception  of  the  camel  family;  in  these 
animals  the  cells  are  oval  in  shape.  In  the  frog  the  red  cells  are 
very  large,  oval,  biconcave  nucleated  cells  and  are  far  larger  than 
the  same  cells  in  man,  measuring  about  24  microns  in  length  and 
14.5  microns  in  width. 

The  size  of  the  red  cell  is  by  no  means  proportionate  to  that  of  the 
animal.  The  musk  deer  possesses  one  of  the  smallest  (2.4  microns); 
in  proteus  the  red  cell  measures  62.5  microns  by  34.5  microns,  while 
in  amphiuma  the  red  cells  are  about  one-third  larger.  That  of  the 
elephant  is  but  9.2  microns  in  diameter  and  beside  it  stands  that  of 
the  humming  bird,  with  a  diameter  of  nearly  9.4  microns. 

The  number  of  red  cells  is  affected  by  altitude;  at  314  meters 
above  sea  level  the  number  is  5,322,000;  at  700  meters  5,900,000; 
at  1800  meters  7.000,000:  at  4392  meters  8,000,000.  This  increase 
is  affected  during  two  or  three  weeks  and  upon  return  to  sea  level 
the  number  gradually  drops  to  5,000,000  again  <K6ppe).  There 
is  apparently  no  difference  of  number  in  the  different  races. 

The  red  cells  are  more  numerous  in  carnivorous  than  in  her- 
bivorous animals,  while  in  birds  they  are  larger  in  size.  In  the 
amphibians,  where  the  size  is  great,  the  number  is  small.  In  the 
dog  the  red  cells  measure  about  7  microns  in  diameter;  in  the  sheep 
5  microns;  in  the  goat  4  microns;  in  birds  8.5  to  14.5  microns. 

According  to  Malassez  and  Hayem,  each  cu.  mm.  of  goat's  blood 
contains  18  to  19  millions  of  red  cells;  birds  2  to  3  millions;  reptiles 
0.5  to  1.6  millions;  frogs  400.000;  proteus  36,000;  bony  fishes  1  to  2 
millions;  torpedo  140,000.  - 


206  PRACTICAL  HISTOLOGY 

The  white  blood  cells,  or  leukocytes  are  large  pale  cells  readily 
distinguised  from  the  above.  They  consist  of  about  90  per  cent, 
water  and  10  per  cent,  of  solids  (proteins,  lecithin,  glycogen,  fat 
and  phosphorus).  About  5000  to  8000  are  found  in  each  cubic 
millimeter  of  blood;  there  is  a  physiologic  increase  at  certain  times, 
after  meals,  especially  those  rich  in  protein  material.  Fasting 
reduces  the  number  and  in  total  abstinence  of  food  the  number  may 
fall  to  1000  per  cu.  mm.  At  birth  they  number  17,000  to  20,000 
per  cu.  mm.  while  in  the  adult  the  number  is  as  above,  or  1  to  every 
700  red  cells.  The  proportion  in  the  splenic  aertery  is  1  to  2260 
red  cells  and  in  the  splenic  vein  1  to  60  red  cells;  in  the  portal 
vein  the  proportion  is  1  to  740  and  in  the  hepatic  vein  1  to  170 
red  cells.  Some  of  the  leukocytes  are  actively  ameboid  and 
phagocytic. 

The  cytoplasm  of  the  leukocytes  is  reticular  even  in  the  living 
cells;  in  addition  granules  of  various  types  may  be  present.  The 
nucleus  varies  from  small  to  large  and  its  stain  reaction  is  not  the 
same  in  all  leukocytes.  Some  are  multinuclear.  A  centrosome  and 
attraction  sphere  are  usually  to  be  found  near  the  nucleus. 

They  are  classified  as  follows: 

1.  Lymphocytes  (small  lymphocytes). 

2.  Hyalin  cells  (large  lymphocytes). 

3.  Polymorphonuclear  leukocytes,  or  finely  granular  oxyphils 
{Formerly  neutrophil) . 

4.  Coarsely  granular  oxyphils  (Formerly  acidophil). 

5.  Finely  granular  basophils. 

6.  Coarsely  granular  basophils. 

1.  The  lymphocytes,  or  microleukocytes,  are  the  smallest  of  the 
white  cells,  average  4.5  to  7.5  microms  in  diameter  and  are  the  first 
to  form.  Each  consists  of  a  large  darkly  staining  nucleus  surrounded 
by  a  narrow  rim  of  faintly  staining  cytoplasm  that  may  be  basophilic 
in  reaction.  The  large  nucleus  is  nearly  spherical  in  form  and  the 
chromatin  is  prominent.  This  variety  is  formed  mainly  in  the 
lymphoid  tissues  and  organs  and  some  arise  in  the  red  bone-marrow. 
This  variety  is  both  ameb old  and  phagocytic  and  constitutes  about 
20  to  25  per  cent,  of  the  white  cells. 


CIRCULATORY   SYSTEM  207 

2.  The  hyalin  cell,  or  macrolymphocyte,  is  the  largest  white  cell 
and  averages  from  n  to  15  microns  in  diameter.  It  is  said  that 
they  are  derived  from  the  lymphocytes  which  they  resemble.  Both 
nucleus  and  cytoplasm  stain  but  faintly,  hence  the  name.  In  the 
cytoplasm  some  basophilic  granules  are  occasionally  seen.  The 
nucleus  is  large,  usually  hazy  in  appearance  and  often  kidney-shaped. 
This  cell  is  actively  ameboid  and  phagocytic.  They  are  found  in 
lymphoid  tissues  and  organs  and  some  are  formed  in  the  red  bone- 
marrow.     They  represent  from  2  to  4  per  cent,  of  the  white  cells. 

3.  The  finely  granular  eosinophils,  or  finely  granular  acidophils 
{polymorphonuclear  neutrophils)  are  the  most  numerous  of  the  white 
cells  and  average  from  7.5  to  10  microns  in  diameter.  There  are 
said  to  be  several  stages  of  this  cell,  the  younger  showing  a  centro- 
some  and  nucleus  that  contains  little  chromatin  and  fewer  modifi- 
cations of  nuclear  shapes,  and  older  ones  that  have  a  dense  chromatic 
network  and  more  varieties  of  nuclear  shapes.  The  latter  may  be 
U,  V,  W,  etc.,  and  may  even  be  divided  into  a  number  of  segments. 
The  younger  cells  are  said  to  be  capable  of  reproducing  to  a  slight 
extent  and  the  older  ones  not  at  all.  The  cytoplasm  contain  a  large 
number  of  fine  granules  that  usually  take  the  plasmatic  stains  quite 
deeply.  These  granules  were  at  one  time  thought  to  be  neutro- 
philic and  the  cells  were  called  neutrophils*  These  cells  are  increased 
in  number  after  a  meal  and  are  formed  in  the  red  bone  marrow. 
They  are  actively  ameboid  and  phagocytic  and  represent  60  to  70  per 
cent,  of  all  of  the  leukocytes.  They  are  the  active  infection  fighters 
of  the  body  and  are  the  chief  cells  seen  in  such  areas. 

4.  The  coarsely  granular  eosinophil,  or  eosinophil  is  7  to  10  microns 
in  diameter.  The  cytoplasm  contains  a  few  large  granules  that 
take  the  plasmatic  stains  very  deeply.  Ehrlich  suggests  that  these 
granules  may  be  zymogen  granules.  The  deeply  staining  nucleus 
may  be  horseshoe-shaped  or  lobulated.  The  younger  cells  contain 
a  centrosome  and  are  capable  of  division  but  the  older  ones  are  not. 
They  are  formed  in  the  red  bone-marrow  and  are  actively  ameboid 
but  not  phagocytic.  They  represent  from  1  to  4  per  cent,  of  the 
white  cells  in  the  child  but  rarely  run  over  2  per  cent,  in  the  adult. 

5.  The  finely  granular  basophil  resembles  group  3  except  that 
the  granules  take  a  basic  stain.     These  are  formed  in  the  red  bone 


208 


PRACTICAL   HISTOLOGY 


marrow  and  are  present  to  the  extent  of  o.i  to  i  per  cent.,  but  are 
usually  under  0.25  per  cent. 

6.  The  coarsely  granular  basophil  is  said  to  be  absent  from  normal 
blood.     They  are  relatively  large  cells  and  are  also  called  mast  cells. 


m 


TV. 


m. 


f>% 


m 


Fig.  130. — The  Blood  Corpuscles.     (Wright's  Stain.)     (£.  F.  Faber,  from 

Da  Costa's  Clinical  Hematology.) 
I,   Red  corpuscles.     II,  Lymphocytes  and  large  mononuclear  leucocytes.     Ill, 

Neutrophiles.     IV,   Eosinophiles.  V,    Myelocytes    (not    found    in    normal 

blood).     VI,    Mast  cells. 

The  cytoplasm  contains  a  number  of  large  coarse  granules  that 
respond  well  to  the  basic  stains.  The  nucleus  stain  readily  and 
varies  in  shape.  They  are  said  to  be  present  to  the  extent  of  0.5 
per  cent.     Some  consider  these  cells  are  eosinophils  in  a  state  of 


CIRCULATORY    SYSTEM 


209 


degeneration;  the  granules  represent  fragments  of  the  nucleus  and 
products  that  are  the  result  of  mucoid  degeneration  of  the  cytoplasm. 
Maximow  considers  them  special  leukocytes.  They  are  formed  in 
the  red  bone-marrow  and  are  also  found  in  areolar  tissue  where  they 
probably  end  their  existence.  In  certain  diseases  they  increase 
in  number  in  the  marrow  and  spleen  and  are  found  in  the  blood  in 
greater  numbers. 

The  leukocytes  are  general  scavengers  as  they  remove  foreign 
bodies,  bacteria  and  disintegrating  tissues.  This  process  is  called 
phagocytosis.  In  their  dissolution  they  contribute  to  the  blood 
plasma  certain  proteins  that  assist  in  the  coagulation  of  the  blood. 


1 

.*  w 

.' 

\     , ' 

1 
c 

*-.      i  , 

'•  ' 

v.. 

■jjB 

1           \ 

■    ! 

m 

;•( 

'  f   X 

1 

1 

1 

1 

> 

Fig.  131. — Blood  Platelets  Showing  Ameboid  Condition  and  Chromidia. 

(.After  Kopsch.) 


Some  leukocytes  are  lost  in  the  alimentary  tract  and  some  are  de- 
stroyed by  the  phagocytes  of  the  spleen,  hemolymph  nodes  and  even 
in  lymph  nodes. 

The  blood  platelets,  or  thrombocytes  are  small,  colorless,  oval  or 
circular  discs.  These  are  capable  of  ameboid  movements  and  measure 
from  1  to  3.5  microns  in  diameter.  The  cytoplasm  is  homogeneous 
or  finely  granular.  Each  possesses  a  chromatin  mass  (chromidium) 
that  apparently  represents  a  nucleus.  In  drawn  blood  these  elements 
collect  in  groups.  They  stain  with  basic  dyes,  especially  methyl 
violet.  They  number  200,000  to  300,000  per  cu.  mm.  They  are 
formed  in  red  bone  marrow  and  are  said  to  be  derived  from  the  myelo- 


14 


210  PRACTICAL  HISTOLOGY 

plaxes  or  megakaryocytes,  as  broken  off  fragments  of  their  pseudo- 
podia.  They  are  readily  found  in  blood  fixed  in  a  i  per  cent, 
solution  of  osmic  acid. 

When  these  cells  come  in  contact  with  a  foreign  body  they  rapidly 
throw  out  processes  and  adhere  to  it.  In  this  way  they  form  a  plug 
and  assist  in  stopping  hemorrhages,  forming  a  while  clot,  or  thrombus. 
They  are  supposed  to  contain  prothrombin  which  becomes  converted 
into  thrombin  or  fibrin  jerment.  In  certain  diseases  these  elements  are 
increased  in  number  while  in  others  they  are  decreased.  According 
to  Helber  blood  platelets  are  not  found  in  the  blood  of  frogs  or  birds. 

The  intercellular  substance,  or  liquor  sanguinis,  contains  the  salts 
of  the  blood.  Its  density  is  such  that  the  cells  retain  their  normal 
shape.  It  consists  of  90  per  cent,  water  and  10  per  cent,  of  pro- 
teins, fats,  sugar,  inorganic  salts,  urea,  cholesterin,  lecithin,  etc. 
It  contains  not  only  nutritious  substances  but  waste  products  and 
the  fibrinogen  in  solution.  If,  however,  solutions  are  added  that 
differ  in  density,  the  action  upon  the  cells  is  characteristic. 

Upon  the  addition  of  strong  {hypertonic)  salt  solution,  the  cells 
become  irregular  in  outline,  and  are  crenated.  If  water  or  salt  solu- 
tions under  0.5  per  cent,  {hypotonic)  be  added,  it  dissolves  the  hemo- 
globin, and  the  cells  swell  and  become  spherical.  These  are  blood 
shadows.  When  these  burst  the  particles  constitute  the  blood 
dust  or  hemokonia  of  Mueller. 

The  action  of  acetic  acid  is  important.  The  addition  of  a  0.3 
per  cent,  solution  decolorizes  the  red  cells  and  renders  the  white  cells 
more  distinct.  This  is  made  use  of  in  hematology  for  the  purpose 
of  counting  the  white  cells,  in  a  fresh  condition. 

An  important  property  of  blood  is  that  of  clotting,  or  coagulation. 
The  fibrinogen  is  precipitated  as  fibrin  and  this  entangles  the  cells. 
As  the  fibrin  contracts  the  liquid  portion  of  the  blood  and  the  salts  are 
separated  as  a  yellowish  fluid  which  is  the  serum.  This  contains  no 
fibrinogen.  The  clot  contains  the  fibrin  and  the  entangled  cells. 
The  precipitation  of  the  fibrinogen  is  due  to  some  agent,  called 
thrombin,  that  is  formed  by  the  leukocytes  in  their  decomposition  or 
dissolution  and  by  the  thrombocytes.  Coagulation  of  the  blood 
may  be  hindered  by  the  addition  of  certain  salts  as  magnesium 
sulphate  and  potassium  oxalate,  or  by  cold.     Clotting  is  hastened  by 


CIRCULATORY   SYSTEM 


211 


stirring,  the  addition  of  foreign  bodies  or  by  keeping  the  blood  at  a 

temperature  of  380  to  5o°C.  The  lack  of  certain  substances  in  the 
blood  leads  to  difficulty  of  coagulation  and  such  persons  are  known  as 
bleeders;  the  condition  is  known  as  hemophilia. 

Hemoglobin  is  an  organic  iron  compound  of  a  globulin  and  as  it 
exists  in  the  blood  it  cannot  readily  be  studied.  In  the  lungs  the 
oxygen  forms  an  unstable  compound  called  oxyhemoglobin  and  in 
the  tissue  spaces  the  affinity  for  or  need  of  oxygen  is  so  great  that 
it  is  readily  removed  from  the  hemoglobin.  The  bright  red  color 
of  blood  of  the  arteries  is  due  to  this  compound.  It  is  probably 
in  solution  in  the  cytoplasm  of  the  erythrocytes  from  which  it  may 
readily  be  removed  by  ether  or  it  can  be  easily  converted  into  a 
crvstallin  form. 


Fig.   132. 

1,  Hemin  crystals  of  man  (X  560);  2,  crystals  of 
common  salt;  3,  hematoidin  crystals  of  man. 
(Slohr's  Histology.) 


Fig.  133.  —  Hemoglobin 
Crystals  of  a  Dog 
(X  100);  a  crystal  sepa- 
rating into  fibers. 
(Slohr's  Histology.) 


Hemoglobin  crystals  will  be  formed  if  a  drop  of  defibrinated  blood 
be  mixed  with  a  drop  of  Canada  balsam,  or  clove  oil,  and  covered 
with  a  cover-glass.  They  are  large,  red,  rhombohedral  crystals  or 
elongated  prisms  in  man. 

Hemin  crystals  may  be  prepared  by  adding  a  small  crystal  of  salt 
and  two  drops  of  glacial  acetic  acid  to  a  little  dried  blood,  and  heating 
until  the  mixture  boils.  During  this  process  it  should  be  covered. 
When  cool,  small  brownish  crystals  {hemin.  chl  or  id)  will  be  found. 
These  may  be  single  or  grouped  in  the  form  of  rosettes,  and  are 
known  as  Teichmanns  crystals.  As  these  crystals  will  form  as 
readily  in  old  dried  specimens  of  blood  as  in  fresh  specimens  this 
test  is  of  importance  medico-legally. 

Hemosiderin  is  a  decomposition  derivative  of  hemoglobin  con- 
taining iron.     These  light  brown  granules  are  found  in  the  bone- 


212  PRACTICAL   HISTOLOGY 

marrow  and  spleen  and  even  in  phagocytes.  Iron  in  the  tissues  and 
iron  pigments  are  no  doubt  derived  from  the  same  source. 

Hemotoidin  is  another  derivative  of  hemoglobin  but  it  contains 
no  iron.  It  can  be  prepared  as  needle-like  crystals  of  a  yellowish 
color.  It  is  found  in  the  spleen,  derived  from  the  disintegrating 
red  cells;  from  the  spleen  it  is  carried  to  the  liver  where  it  is  utilized 
as  bilirubin. 

Among  other  blood-making  organs  are  placed  the  coccygeal 
and  intercarotid  glands  and  hemolymph  nodes. 

Luschka's  gland  (2.5  mm.  in  diameter),  is  found  in  front  of  the 
tip  of  the  coccyx,  and  is  connected  with  the  middle  sacral  artery. 
It  is  surrounded  by  a  fibrous  sheath,  which  sends  in  septa  that 
divide  the  organ  irregularly  into  areas,  or  compartments.  The 
latter  contains  groups  of  polyhedral  cells  surrounded  by  dense 
plexuses  of  capillaries  of  the  sinusoidal  type.  The  cells  consist  of  a 
finely  granular  cytoplasm  and  a  palely  staining  nucleus.  Many 
of  the  cells  contain  a  yellowish  pigment  that  gives  the  chromaffin 
reaction.     Amyelinated  nerve  fibers  are  numerous. 

The  intercarotid  gland  is  found  at  the  bifurcation  of  the 
common  carotid  artery,  and  its  structure  is  similar  to  that  of 
Luschka's  gland. 

Hemolymph  (Hemal)  Nodes. — These  organs  vary  in  size  from 
a  pin  head  to  a  large  bean  and  are  found  in  abundance  in 
the  retroperitoneal  and  cervical  regions  and  less  numerous  else- 
where. Each  is  surrounded  by  a  capsule  of  white  fibrous  and  yellow 
elastic  tissues,  containing  a  little  smooth  muscle  tissue;  trabecular  pass 
in  and  form  the  framework  of  the  organ.  In  the  framework  are 
found  red  and  white  blood-cells.  Of  the  latter,  the  lymphocytes  are 
the  more  numerous;  besides  these  hyalin,  finely  granular  oxyphils 
and  basophils  are  found  in  varying  numbers.  Megakaryocytes  are 
also  found  here.  In  addition,  mononuclear  phagocytes  that  con- 
tain pigment  and  disintegrating  red  cells  are  seen.  Beneath  the 
capsule  and  following  the  trabecular  to  the  hilus  are  seen  sinuses, 
often  very  large,  that  do  not  contain  lymph  but  blood. 

These  organs  usually  possess  no  lymphatics.  The  blood-vessels 
enter  at  the  hilus  and  form  capillaries  within  the  organ;  these  cap- 
illaries communicate  with  the  blood  sinuses.     The  large  veins  are  in 


CIRCULATORS    SYSTEM  213 

the  trabecular  and  begin  in  thin-walled  lacunae  that  possess  per- 
forated walls,  by  means  of  which  they  communicate  with  the  blood 
sinuses. 

Certain  atypic  organs  possess  lymphatics.  Some  of  these  struc- 
tures resemble  the  spleen  in  structure,  others  the  marrow  and  still 
others  ordinary  lymph  nodes. 

Nerves  are  present  and  probably  pass  to  the  smooth  muscle  tissue. 

Parasympathetics,  or  Aortic  Bodies. — These  are  two  to  four  brown- 
ish bodies  found  in  the  neighborhood  of  the  inferior  mesenteric 
artery  and  closely  related  with  the  aortic  sympathetic  plexus.  Each 
is  surrounded  by  a  capsule  of  white  fibrous  connective  tissue  that 
sends  in  trabecular  that  form  the  framework  of  the  organ.  In  the 
meshes  of  this  framework  are  found  the  epithelium  which  consists  of 
groups  of  polygonal  or  cuboidal  cells  closely  packed  and  of  the  chrom- 
affin type  resembling  the  cells  of  the  medulla  of  the  adrenal. 
These  structures  are  found  only  in  childhood  and  are  supposed  to  be 
accessory  in  function  to  the  adrenals. 

The  blood-vessels  derived  from  the  aorta,  or  inferior  mesenteric 
artery,  follow  the  trabecular  and  form  a  rich  capillary  plexus  around 
the  epithelial  cell-groups. 

The  nerves  are  from  the  sympathetics  and  their  relation  and  ar- 
rangement are  similar  to  the  nerves  of  the  medulla  of  the  adrenal. 

HEMAPOIESIS 

In  the  adult  the  formation  of  red  blood-cells  is  carried  on  chiefly 
by  the  red  bone-marrow;  the  white  blood-cells  are  formed  in  the 
lymphatic  tissues  and  organs  and  to  some  extent  in  the  red  bone- 
marrow.  In  the  fetal  condition  blood-cells  are  made  in  a  number  of 
places;  the  yolk-sac  is  the  seat  of  origin  of  the  first  blood-cells;  then 
the  somatic  mesenchyme  and  primitive  endothelium  of  the  vessels; 
later  the  spleen,  liver,  developing  lymphatic  organs  and  the  bone- 
marrow. 

Two  theories  are  given  as  to  the  origin  of  the  red  and  white  cells; 
the  monophyletic  theory  is  that  all  the  cells  have  a  common  ancestor, 
the  hemoblast,  or  hemogonium;  the  polyphyletic  theory  is  that  the  red 
cells  have  one  ancestor  and  the  white  cells  a  different  original  mother 


214  PRACTICAL  HISTOLOGY 

cell.    Later  investigation  seems  to  indicate  that  the  monophyletic 
theory  is  the  right  one. 

In  the  development  and  differentiation  of  these  cells  the  primitive 
mother  cell  divides  into  two  daughter  cells;  one  of  these  cells  con- 
tinues its  function  as  a  mother  cell  and  the  other  is  an  hemoblast. 
The  hemoblasts  are  probably  carried  by  the  blood-stream  to  the 
organs  that  are  to  serve  an  hemapoietic  function,  where  they 
proliferate.  In  certain  organs  they  persist  throughout  life  but  in 
those  that  have  only  a  temporary  function  of  this  nature  they  ulti- 
mately disappear  therefrom  when  that  function  ceases. 

According  to  Maximow  the  nucleated  red  cells  are  called  ery- 
throcytes and  the  non-nucleated  cells,  erythroplastids.  According 
to  him  the  erythrocytes  are  of  two  kinds;  the  primitive  form  that 
does  not  last  long  and  soon  disappears  and  the  definite  form  that 
consists  of  cells  a  little  smaller  than  the  preceding  and  that  persist 
and  that  give  rise  to  all  of  the  red  cells. 

When  the  hemoblast  divides,  one  of  the  daughter  cells  continues 
the  function  of  the  mother  cell  and  the  other  undergoes  mitosis. 
One  of  its  daughter  cells  is  the  primitive  erythrocyte  and  the  other  is 
called  the  primitive  lymphocyte. 

The  primitive  erythrocyte  is  about  n  microns  in  diameter  and 
continues  to  divide  for  a  while  but  dies  out  in  early  embryological 
stages. 

The  primitive  leukocyte  is  about  9.5  microns  in  diameter  and  the 
cytoplasm  contains  some  basophilic  granules.  Each  divides  and 
one  of  the  daughter  cells  is  the  megaloblast,  the  ancestor  of  the  con- 
tinued red  cells,  and  the  other  is  the  lymphocyte,  the  ancestor  of  the 
various  leukocytes. 

The  megaloblast  is  about  8  microns  in  diameter  and  the  cytoplasm 
contains  only  a  small  amount  of  hemoglobin;  the  large  vesicular 
nucleus  contains  only  a  small  amount  of  chromatin.  This  is  the 
ichthyoid  stage  of  Minot.  The  daughter  cells  of  the  megaloblasts 
are  called  normoblasts.  These  cells  are  somewhat  smaller  than  their 
mother  cell,  the  hemoglobin  is  greater  in  quantity  and  the  nucleus 
strains  more  deeply,  due  to  a  greater  quantity  of  chromatin  being 
present.  This  is  the  sauroid  stage  of  Minot.  The  daughter  cells 
of  the  normoblasts  are  called  erythroblasls.     These  cells  contain  more 


CIRCULATORY   SYSTEM 


215 


hemoglobin  than  their  mother  cells 
(normoblasts)  and  the  nucleus  is 
smaller  and  denser.  By  a  loss  of  its 
nucleus  the  erythroblast  becomes  the 
erythroplasia1.  According  to  some  in- 
vestigators the  nucleus  is  absorbed 
(karyolysts);  according  to  others  it  is 
extruded  in  mass  or  in  fragments 
ikaryorrhexis);  in  the  pig  the  nonnu- 
cleated  red  cells  are  derived  from  the 
erythroblasts  by  a  process  of  budding, 
the  bud  containing  no  nucleus. 

The  lymphocyte,  the  other  daughter 
cells  of  the  primitive  lymphocyte,  is 
the  ancestor  of  the  white  blood-cells. 
One  of  its  daughter  cells  is  called  a 
lymphocyte  and  the  other  a  leukoblast. 
The  lymphocyte  represents  the  large 
lymphocyte  of  the  blood  and  is  ap- 
parently only  a  slightly  modified  orig- 
inal lymphocyte.  When  these  cells 
divide  the  small  daughter  cells  are  the 
small  lymphocytes  of  the  blood;  as  these 
grow  they  become  the  large  lymphocytes. 
From  the  lymphocytes  megakaryocytes 
are  also  differentiated.  These  giant 
cells  are  14  to  20  microns  in  diameter, 
multinuclear  and  give  rise  to  the 
platelets. 

The  leukoblast  gives  rise  to  daughter 
cells  which  by  differentiation  become 
the  myelocytes  and  the  granular  and 
neutrophilic  leukocytes. 

The  accompanying  diagram  will  show 
the  derivatives  of  the  hemoblasts. 


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CHAPTER  VIII 
THE  LYMPHATIC  SYSTEM 

The  lymphatic  system  includes  the  lymphatic  and  thoracic  ducts, 
intermediate  vessels,  capillaries,  lymph  spaces,  lymph  and  a  number 
of  organs,  lymph  nodes  (lymphatic  gland),  spleen,  tonsils  and  thymus 
body. 

The  lymph  consists  of  94  per  cent,  of  water,  3  to  4  per  cent,  of 
proteins  and  the  remainder  of  sugar,  inorganic  salts,  fatty  substances, 
urea,  also  free  oxygen,  carbon  dioxid  and  waste  products.  It  is 
neutral  in  reaction  and  is  derived  from  the  blood  by  osmosis  or 
diffusion  and  is  returned  to  the  blood.  The  lymph  in  the  intercellu- 
lar spaces  carries  oxygen  and  nutritious  materials  to  the  cells  and 
receives  the  carbon  dioxid  and  waste  products.  It  then  enters  the 
lymph  capillaries  (passing  through  their  endothelial  walls) ,  then  into 
larger  vessels  and  ultimately  is  emptied  into  the  venous  blood  at  the 
right  and  left  subclavian-jugular  vein  junctions.  The  cellular  ele- 
ments are  leukocytes ;  these  are  mainly  small  lymphocytes.  They  are 
passed  into  the  blood  in  great  numbers  all  of  the  time;  some  are 
destroyed  and  others  are  said  to  develop  into  other  varieties  of 
leukocytes.  The  leukocytes  tend  to  adhere  to  the  walls  of  the 
vessels  in  the  circulating  current.  As  lymph  contains  fibrinogen  it 
may  readily  clot;  this  clot  is  white  and  the  leukocytes  entangled  in 
the  fibrin  are  toward  the  surface  of  the  clot  (postmortem). 

In  the  lymph  vessels  of  the  small  intestine,  after  absorption,  the 
lymph  contains  a  great  deal  of  fat  in  the  form  of  small  droplets; 
the  lymph  here  has  a  whitish  color  and  is  called  chyle. 

The  lymph  starts  in  the  intercellular  spaces.  These  are  merely 
the  tissue,  or  pericellular  spaces  and  they  are  not  lined  by  endothelial 
cells;  such  spaces  are  found  between  the  epithelial  cells  of  mucous 
membranes  and  glands;  in  the  connective  tissues,  as  the  lacunae  of 

216 


rHE    LYMPHA  tlC  SYSTEM  2  I  7 

bone  and  cartilage  and  cornea,  etc.;  between  the  muscle  fibers. 
They  are  readily  outlined  by  the  silver  nitrate  method. 

The  first  vessels  of  the  lymphatic  system  are  the  capillaries. 
These  are  much  larger  than  those  of  the  blood-vascular  system, 
measuring  from  30  to  60  microns  in  diameter;  the  diameter,  how- 
ever, is  not  constant  as  these  vessels  present  successive  dilatations 
and  constrictions  giving  them  a  varicose  appearance.  The  wall 
consists  of  a  single  layer  of  endothelial  cells  with  very  sinuous 
outlines.  The  layer  of  cytoplasm  is  thin  and  the  nuclei  project 
somewhat.  These  capillaries  are  closed  at  one  end  and  continue 
into  larger  vessels  at  the  other,  so  that  the  lymphatic  system  must 
be  regarded  as  a  closed  system.  Ordinarily  the  capillaries  form  a 
meshwork  but  in  certain  regions,  as  the  villi  of  the  small  intestine, 
they  are  individual,  straight,  blind  tubules  and  are  called  the  lacteah. 

As  the  lymph  capillaries  increase  in  diameter  the  endothelial  tube 
becomes  strengthened  by  the  addition  of  a  delicate  fibro-elastic 
network.  When  they  reach  a  diameter  of  from  0.2  to  0.8  mm. 
they  have  three  coats,  resemble  venules  and  constitute  small  lymph 
vessels.  The  tunica  intima  consists  of  a  single  layer  of  endothelial 
cells  resting  upon  the  fibro-elastic  subendothelial  connective  tissue. 
In  this  the  elastic  fibers  have  mainly  a  longitudinal  direction  but 
interlace  somewhat.  If  the  surrounding  tissue  contains  a  consider- 
able amount  of  elastic  tissue  then  this  tissue  may  be  absent  in  the 
vessel.  The  thin  media  contains  some  circularly  arranged  smooth 
muscle  tissue.  The  adventitia  is  the  thickest  coat  and  consists  of  a 
network  of  fibro-elastic  tissue  in  which  there  may  be  some  smooth 
muscle  tissue  longitudinally  arranged. 

The  large  vessels,  or  lymphatic  ducts,  resemble  veins  more  than 
they  do  arteries.  The  tunica  intima  is  like  that  of  the  smaller 
vessels  but  the  elastic  tissue  is  usually  prominent.  The  tunica 
media  consists  of  fibro-elastic  and  muscle  tissues;  the  muscle  -tissue 
consists  of  smooth  muscle  (more  than  in  a  vein)  circularly  and 
obliquely  arranged.  The  elastic  fibers  are  mainly  circularly 
directed.  The  adventitia  is  quite  thick  and  the  elastic  and  muscle 
fibers  are  chiefly  longitudinally  arranged. 

Blood-vessels  and  nerves  are  abundant  in  the  medium  and  large- 
sized  lymph  channels. 


2l8 


PRACTICAL  HISTOLOGY 


Like  veins  the  lymphatic  vessels,  including  the  lacteals,  possess 
valves.  These  valves  have  the  same  structure  as  those  of  veins  but 
are  placed  at  more  frequent  intervals.  They  are  numerous  in  the 
vessels  of  the  mesentery. 

Lymph  vessels  are  found  in  all  vascular  structures  except  the 
eyeball,  internal  ear  and  the  central  nerve  system;  they  are  also 
absent  from  nails,  hairs  and  cartilage. 

The  lymphatic  structures  comprise  lymphoid  tissue,  including  the 
lymph  nodes,  the  spleen,  thymus  and  tonsils. 


Fig.  134. — Diaphragmatic    Pleura    Showing    Part    of    a   Lymph    Vessel, 
c    c.  Intercellular  spaces;  I,  I.  lymph  vessels  showing  the  outlines  of  the  endo- 
thelial cells.     {After  Ranvier.) 


Lymphoid  tissue  is  arranged  in  four  forms,  diffuse,  solitary 
nodules,  agminated  nodules  and  lymph  nodes. 

Diffuse  lymphoid  tissue  is  an  indefinite  collection  of  leukocytes 
in  an  organ.  It  is  found  in  the  tunica  propria  of  the  alimentary,  res- 
piratory and  urinogenital  tracts.  It  forms  the  medulla  of  the  1  obules 
of  the  thymus  body  and  the  bulk  of  the  spleen  and  tonsils.  In  the 
former  places  it  consists  merely  of  the  leukocytes  scattered  in  the 
areolar  tunica  propria.  The  number  is  usually  so  great  that  this 
tissue  has  a  dark  appearance  and  the  connective-tissue  portion  is 
hidden.     Under  a  low  magnification  the  tunica  propria  has  a  granular 


THE    LYMPHATIC   SYSTEM 


2IQ 


appearance.  In  the  spleen,  thymus  and  tonsils  the  supportive  tissue 
is  the  reticulum  of  the  organ.  The  cellular  elements  are  mainly 
small  and  large  lymphocytes,  only  a  few  of  the  other  varieties  of 
leukocytes  being  present. 

Solitary  nodules  are  small  dense  collections  of  small  and  large 
lymphocytes  sharply  outlined,  usually,  from  the  surrounding  tissue. 


Fig.  135. — Section  of  the  Mucosa  of  the  Jejunum  of  the  Cat. 

a,  Simple  columnar  and  goblet  cell  layer  separated  from  the  core  of  the  villus  b', 
the  latter  is  filled  with  diffuse  lymphoid  tissue,  c,  Simple  tubular  glands 
with  the  intervening  tunica  propria  filled  with  diffuse  lymphoid  tissue. 
(Photograph.     Obj.  16  mm.  oc.  7.5  X-) 


The  supportive  tissue  is  said  to  be  reticulum,  the  meshes  of  which 
are  larger  in  the  germinal  center  than  at  the  periphery.  The  center 
of  a  nodule  is  usually  lighter  and  is  called  the  germinal  center;  here 
the  cells  are  fewer  in  number,  more  widely  separated  and  younger. 
This  is  the  area  where  the  cells  undergomitotic^  division.  As  the 
new  cells  are  formed  the  excess  cells  are  crowded  and  packed  at  the 


2  20  PRACTICAL   HISTOLOGY 

periphery  of  the  nodule.  As  they  form  a  dense  mass  they  give  to 
the  periphery  of  the  nodule  a  darker  appearance.  In  general  appear- 
ance the  lobules  of  the  thymus  body  are  merely  very  large  and 
irregular  solitary  nodules. 

These  structures  are  found  in  the  submucous  coat  of  the  ali- 
mentary and  respiratory  tracts  and  in  the  spleen  and  tonsils. 
These  and  the  diffuse  variety  are  transient  «in  character. 


Fig.  136.— Solitary  Nodule  of  the  Spleen  of  a  Monkey. 
The  light  area  is  the  germinal  center.     The  nodule  is  surrounded  by  diffuse 
lymphoid  tissue.     (Photograph.     Obj.  16  mm.  oc.  7.5  X-) 

The  agminate  nodules,  or  Peyer's  patches,  are  more  or  less  regular 
collections  of  solitary  nodules  forming  an  individual  mass,  sharply 
outlined  from  the  surrounding  tissues.  Each  patch  is  from  1  to 
5  cm.  in  length  and  consists  of  from  ten  to  sixty  nodules,  each  of 
which  shows  a  germinal  center.  Each  nodule  is  partially  or  com- 
pletely surrounded  by  a  delicate  capsule  of  white  fibrous  tissue, 
although  usually  the  nodules  merge  more  or  less  into  one  another. 
They  are  located  in  the  submucosa  of  the  ileum  opposite  to  the 
attachment  of  the  mesentery.  Some  state  that  they  are  also  found 
in  the  jejunum.     The  long  axis  of  each  is  directed  parallel  to  the 


THE    LYMPHATIC   SYSTEM 


221 


long  axis  of  the  bowel.  They  are  visible  to  the  unaided  eye.  Al- 
though they  are  said  to  be  loea ted  in  the  submucosa,  more  commonly 
they  are  seen  invading  the  mucosa,  having  broken  through  the 
muscularis  mucosae.  Usually  in  those  areas  where  the  nodules 
approach  the  epithelial  surface,  the  glands  are  absent.  At  the  edges 
of  the  nodules  the  glands  are  seen  arranged  in  the  form  of  a  circle. 
Often  the  villi  are  absent  over  such  an  area. 

Each  nodule  has  a  thin- walled  artery  that  passes  to  the  center  and 
forms  a  capillary  plexus  of  wide  meshes.  These  extend  to  the 
periphery  where  the  blood  is  collected  by  two  or  more  small  veins. 


Fig.  137. — An  Agminated  Nodule  of  the  Ileum  of  a  Cat. 
(Photograph.     Obj.  48  mm.) 


Lymph  nodes,  or  glands,  are  bean-shaped  organs  placed  in  the 
pathways  of  the  lymph  vessels  so  that  the  lymph  must  filter  through 
one,  or  usually  more,  of  these  structures  before  it  ultimately  enters 
the  blood  stream.  They  vary  in  size  from  a  few  millimeters  to 
several  centimeters  in  length.  They  are  found  distributed  over  the 
body  but  are  more  numerous  in  the  trunk.  They  are  most  numerous 
in  mammals,  a  few  are  found  in  birds,  but  none  are  found  in  the  lower 
vertebrates.  Each  is  surrounded  by  a  capsule,  has  a  hilus  and 
consists  of  cortex  and  medulla. 

The  capsule  consists  of  a  thin  layer  of  white  fibrous  connective 
tissue  containing  yellow  elastic  fibers  and  smooth  muscle  tissue. 
Between  it  at  the  parenchyma  is  seen  a  lymph  space,  the  sinus, 
exhibiting  a  network  of  reticulum,  that  is  continuous  with  the 
reticulum  of  the  organ,  on  the  one  hand,  and  attached  to  the  capsule, 
on  the  other.     At  regular  intervals  the  inner  surface  of  the  capsule 


222 


PRACTICAL   HISTOLOGY 


sends  into  the  peripheral  portion  of  the  organ,  trabecule  or  partial 
septa  covered  with  endothelial  cells.  These  divide  the  outer  part 
of  the  parenchyma  into  a  number  of  nearly  uniform  masses  called 
the  secondary  nodules;  these  and  the  trabecular  constitute  the  cortex 
of  the  node.  The  lymph  sinus  continues  along  the  trabeculae. 
Within  the  organ  the  trabeculae  continue  into  the  central  part  or 
medulla  where  they  form  a  large  coarse  meshwork  for  the  support 
of  the  larger  vessels.  Throughout  the  organ  the  spaces  between  the 
trabeculae  and  capsule  contain  a  delicate  meshwork  of  reticulum 


A 

Fig.   138. — Longitudinal  Section  of  a  Lymph  Node. 
a,  Hilus;  b,  arteriole;  c,  venous  sinuses;  d,  adipose  tissue;  e,  secondary  nodule 
of  cortex;  /,  vein  in  medulla;  g,  subcapsular  lymph  sinus;  h,  germinal  center 
of  secondary  nodule;  1,  i,  trabeculae;  k,  capsule;  /,  lymph  sinus;  m,  medullary 
cord. 

that  constitutes  the  finer  framework  of  the  organ.  This  is  for  the 
support  of  the  capillary  vessels  and  the  functionating  cells  of  the 
organ.  The  reticulum  cells  are  attached  to  the  reticulum  fibers  and 
are  said  to  be  phagocytic  and  contain  pigment  granules  and  even 
erythrocytes.     The  trabeculae  contain  some  smooth  muscle  fibers. 

The  cortex  comprises  the  secondary  nodules,  the  trabeculae  and  the 
peripheral  portion  of  the  lymph  sinus.  The  secondary  nodules  are 
from  0.5  to  1  mm.  in  diameter  and  are  just  beneath  the  capsule  and 


THE   LYMPHATIC   SYSTEM  223 

are  separated  from  one  another  by  the  trabecular  and  the  sinus. 
Each  is  a  solitary  nodule  presenting  a  germinal  center  and  a  darker 
peripheral  zone  where  the  lymphocytes  are  closely  packed.  The 
central  lymphocytes  show  mitotic  figures.  The  germinal  centers 
are  not  distinct  in  very  young  or  old  animals.  Laterally  the  nodules 
may  connect  with  one  another.  The  medullary  side  of  each  nodule 
continues  as  a  cord-like  mass  into  the  center  of  the  organ  where  they 
anastomose  or  join  one  another.  These  are  the  medullary  cords. 
The  cells  are  chiefly  lymphocytes,  which  are  arranged  in  concentric 
layers  around  the  periphery  of  each  nodule.  Other  cells  of  the 
hyalin  variety  are  found  in  the  center  of  each  nodule.  During 
gestation  nucleated  red  blood-cells  may  be  present. 

The  medulla  consists  of  the  medullary  cords,  the  trabecidez  and  a 
continuation  of  the  sinus.  It  is  best  developed  in  the  mesenteric 
and  lumbar  lymph  nodes. 

The  medullary  cords  are  the  cord-like  continuations  of  the  cortical 
nodules.  Within  the  reticular  and  trabecular  network  of  the  me- 
dulla these  cords  anastomose  and  join  one  another  to  form  a  darkly 
staining  coarse  meshwork  of  dense  lymphoid  tissue.  They  consist 
of  a  reticulum  supporting  the  lymphocytes  and  blood-vessels.  Be- 
tween the  medullary  cords  the  tissue  is  lighter.  Here  are  seen  the 
band-like  trabecular  continued  from  the  cortex.  Each  consists  of 
rather  dense  white  fibrous  tissue  containing  some  smooth  muscle 
tissue.  Between  the  trabecular  and  the  medullary  cords  is  seen  a 
delicate-  reticulum  that  marks  the  position  of  the  sinus  continued 
from  the  cortex.  As  has  been  shown  the  sinus  is  not  a  clear-cut  space 
but  a  series  of  fine  spaces  between  the  trabecular  and  the  parenchyma 
of  the  organ 

At  one  side  of  a  lymph  node  is  a  scar-like  depression  called  the 
hilus.  Here  the  cortex  is  absent  and  the  medulla,  mainly  white 
fibrous  tissue,  comes  to  the  surface.  It  is  also  the  region  where 
some  of  the  vessels  enter  and  most  of  them  leave. 

The  cells  are  mainly  small  lymphocytes  and  then  the  hyalin 
cells  are  next.  Both  of  these  varieties  are  seen  undergoing  mitosis 
especially  in  the  germinal  centers  of  the  nodules.  A  few  finely 
granular  oxyphils,  eosinophils  and  mast  cells  occur  in  these  organs 
but   they  are  probably  not  formed  here  in  any  great  numbers. 


224  PRACTICAL   HISTOLOGY 

Many  of  these  cells  may  contain  fat,  red  cells,  pigment  granules  and 
bacteria. 

The  arterial  vessels  enter  at  the  hilus  and  divide  into  branches 
some  of  which  continue  into  the  trabecular  to  the  cortex  where 
they  pass  to  the  nodules  and  form  a  capillary  plexus  in  these  struc- 
tures. Others  pass  directly  to  the  capsule  for  its  nourishment. 
Other  branches  leave  the  trabecular  just  within  the  hilus  and  pass 
to  the  medullary  cords  where  a  capillary  meshwork  is  formed.  The 
blood  is  collected  by  veins  that  carry  the  blood  to  the  hilus  where 
one  or  more  vessels  leave.  A  few  small  arterioles  may  enter  at 
the  capsule. 

The  afferent  lymph  vessels  all  enter  at  the  surface  and  open  directly 
into  the  capsular  lymph  sinus.  The  lymph  then  filters  through 
the  reticulum  of  the  sinus  and  its  medullary  extensions  toward 
the  hilus  where  the  lymph  is  collected  into  one  or  more  efferent 
vessels. 

The  nerves  are  not  numerous.  Myelinated  and  amyelinated  nerve 
fibers  form  plexuses  around  the  vessels  and  supply  the  muscle 
tissue  of  these  and  the  trabecular.  They  have  not  been  demon- 
strated in  the  nodules  or  cords. 

Lymph  nodes  are  the  highest  form  of  lymphoid  tissue.  They  are 
often  collected  into  groups  as  in  the  axilla,  femoral  and  inguinal 
regions.  They  are  said  to  be  somewhat  inconstant  as  they  may 
disappear  early  or  change  from  place  to  place.  They  make  certain 
kinds  of  white  cells,  filter  the  lymph  and  are  the  centers  of  cell 
destruction,  and  in  the  female,  during  pregnancy  they  may  form 
red  blood-cells. 

Hemolymph  nodes  have  been  described  under  the  circulatory 
system. 

THE  SPLEEN 

The  spleen  is  the  largest  of  the  lymphoid  structures  and  is  located 
in  the  abdominal  cavity.  It  is  a  soft  organ  of  a  dark-red  color  and 
its  shape  depends  upon  the  state  of  the  organs  surrounding  it. 
It  is  surrounded  by  a  capsule  that  is  invested  with  peritoneum; 
within  this  is  the  splenic  substance  consisting  of  the  splenic  pulp 
and  the  splenic  corpuscles. 


THE    LYMPHATIC    SYSTEM 


225 


The  capsule  is  a  rather  thick  layer  of  dense  white  fibrous  tissue 
containing  elastic  fibers  and  a  considerable  quantity  of  smooth 
muscle  tissue.  Externally  the  capsule  is  covered  by  the  peritoneum 
which  is  a  serous  membrane.  This  consists  of  a  single  layer  of 
endothelial  cells  that  rest  upon  a  thin  layer  of  fibroelastic  tissue. 
This  is  thinner  than  the  capsule  proper.  From  the  inner  surface  of 
the  capsule  beams  of  white  fibrous  tissue  extend  into  the  organs 


^*%7Z?%   ■  :.       iff     1?.-'V.    \   .'  , 


B 


Fig.   139. — Section  of  Spleen. 
a.    Capsule;   6,   trabecule,   longitudinal  section;   c,  pulp;   d,  splenic  corpuscle; 
e,  germinal  center  of  corpuscle;  /,  eccentric  arteriole  in  corpuscle;  g,  trabecula, 
cross-section;  h,  blood-vessel. 


and  form  a  coarse  meshwork.  These  trabecular  contain  smooth 
muscle  tissue  and  blood-vessels.  The  arterial  vessels  are  thicker- 
wall  and  smaller  in  caliber  than  the  veins.  Within  the  large  meshes 
made  by  the  trabecular  there  is  a  delicate  network  of  reticulum. 
This  is  for  the  support  of  the  splenic  substance  and  the  smaller 
vessels.     Upon  this  reticulum  phagocytic  reticulum  cells  are  found. 

The  splenic  substance  comprises  the  pulp  and  the  splenic  corpuscles. 

The  splenic  pulp  consists  of  diffuse  lymphoid  tissue  comprising 
lymphocytes,  hyalin  cells  and  polynuclear  cells;  the  large  cells  are 
15 


226 


PRACTICAL  HISTOLOGY 


the  most  numerous.  In  addition  there  are  a  few  nucleated  red 
cells,  a  great  many  thrombocytes,  erythrocytes  and  many  disinte- 
grating red  cells.  The  large  number  of  red  cells  in  the  pulp  gives 
the  color  to  the  spleen.  The  presence  of  nucleated  red  cells  in  the 
adult  condition  is  denied  by  some.  In  fetal  life  and  sometimes  early 
childhood  nucleated  red  cells  may  be  numerous.     The  splenic  phag- 


m 


|«v;i, 


-r*0 


fk 


A  a 

Fig.  140. — Reticular  Tissue  Seen  in  a  Frozen  Section  of  a  Dog's  Spleen 
Which  Had  Been  Injected  with  Silver  Nitrate.      X  250.     (Mall.) 
A,  Artery  with  its  ampullae  (a);   V,  vein. 


ocytes  are  large  polynuclear  cells  that  are  ameboid  as  well  as  phag- 
ocytic; their  cytoplasm  usually  contains  many  pigment  granules 
and  often  erythrocytes  that  are  undergoing  disintegration.  Some 
giant  cells,  or  megakaryocytes  are  present.  These  are  especially 
numerous  in  the  fetal  condition  and  some  claim  that  in  the  adult 
they  are  absent  from  the  spleen.  The  large  number  of  disinte- 
grating red  cells  in  the  splenic  pulp  has  led  some  to  call  the  spleen 


THE   LYMPHATIC   SYSTEM 


227 


the  graveyard  of  the  erythrocytes.  The  uneven  mixture  of  nucle- 
ated and  nonnucleated  elements  gives  the  stained  sections  of  the 
spleen  a  characteristic  mottled  appearance. 

The  splenic,  or  Malpighian  corpuscles  are  dense  collections  of  lym- 
phoid tissue.     Each  is  really  a  solitary  nodule  in  which  is  usually 


Terminal  vein. 


Pulp  vein. 


Beginning  of  a 
trabecular  vein. 


Capillaries  of 
a  nodule. 


Sheathed  artery.        Pulp  artery. 


Trabecula. 


Penicillus. 


Central  artery 


Trabecular  vein 


Trabecular 
artery. 


Splenic 
lobule. 


Hilus 


Reticulum.       Splenic  nodule. 


Capsule. 


Fig.  141. — Diagram  of  the  Blood  Vessels  of  the  Human  Spleen. 

{Lewis  and  Stohr.) 

At  x  is  shown  the  direct  connection  of  terminal  arteries  with  terminal  veins  (the 
existence  of  such  a  connection  has  been  questioned).  At  xx  and  xxx  are 
the  free  endings  of  the  terminal  veins  in  the  pulp  and  near  the  nodules 
respectively. 


seen  an  eccentrically  placed  arteriole.  These  vessels  are  not  found 
in  the  ordinary  solitary  nodules  and  so  this  is  characteristic  of  the 
structure  of  the  nodules  of  the  spleen.  Each  nodule  usually  shows 
a  germinal  center.  It  represents  a  collection  of  lymphocytes  in 
the  adventitial  sheath  of  the  arteriole. 


228 


PRACTICAL   HISTOLOGY 


The  circulatory  system  of  the  spleen  is  peculiar  in  being  an  open 
one.  Capillaries  as  such  do  not  exist  and  the  arterioles  and  venules 
are  connected  to  each  other  by  blood-spaces  or  ampullae.  The  walls 
of  these  vessels  are  said  to  be  porous. 

The  blood-vessels  enter  and  leave  at  the  hilus.  The  splenic  artery 
divides  into  six  or  more  branches.  As  these  arteries  enter  the 
spleen  they  branch  and  of  these  divisions  some  enter  the  pulp  almost 
immediately  while  others  follow  the  trabecular  to  their  smallest 


Capsule. 


Intralobular  trabecula. 


Artery  to  one  of  the  ten  : *!■ — ; 

compartments.  v 

Intralobular  artery.  j  - 


Interlobular  trabecula.  \- 


Intralobular  trabecula 
Malpighian  corpuscle.  \ 


-  Intralobular  venous 
spaces. 

'•—  >^s"r-^- 1  Intralobular  vein. 

/< Ampulla  of  Thoma. 


\£ Spleen  pulp  cord. 

r-  Interlobular  vein. 

:  Intralobular  vein. 


Fig.    142. — Diagram   of  Lobule   of   the   Spleen.     (Mall,    "Johns   Hopkins 
Hospital  Bulletin,"  Sept.,  Oct.,  1898.)      (Bohm  and  Davidoff.) 


divisions  and  to  the  capsule.  The  adventitia  of  the  small  arterioles 
in  the  pulp  contains  some  lymphoid  cells  and  is  then  called  the 
lymphoid  sheath.  At  frequent  intervals  the  lymphoid  tissue  becomes 
very  abundant  forming  spherical,  or  oblong  masses  called  the  splenic 
corpuscles.  These  corpuscles  receive  capillaries  from  the  enclosed 
arteriole.  The  arterioles  after  leaving  the  corpuscles  divide  into 
branches  which  are  said  to  be  surrounded  by  the  ellipsoidal  sheaths ; 
these  are  said  to  be  condensations  of  the  reticulum,  without  leuko- 
cytes, surrounding  the  terminal  arteriole  branches.  These  branches 
then  end  in  the  so-called  capillaries  that  are  really  dilated  channels 


THE    LYMPHATIC    SYSTEM  229 

the  walls  of  which  are  not  complete.  Some  state  that  the  capillary 
tubes  end  by  opening  directly  into  the  pulp  and  that  the  terminal 
cells  of  these  capillaries  have  branched  processes  that  join  those  of 
the  reticulum  cells  of  the  pulp.  The  blood  is  thus  emptied  directly 
into  the  pulp  spaces.  The  veins  start  in  this  manner  as  venous 
sinuses  and  these  are  surrounded  by  ring-like  collections  of  reticulum 
fibers  and  some  longitudinal  fibers  that  cause  a  ribbing  of  the  sinus 
walls.  The  small  veins  quickly  enter  the  trabecular  and  through 
them  join  to  form  larger  vessels  that  proceed  toward  the  hilus  to 
form  the  single  splenic  vein. 

According  to  Mall  the  spleen  is  divided  into  circulatory  lobules, 
about  one  mm.  in  diameter,  each  one  of  which  is  further  subdivided 
into  histologic  units,  one  for  each  terminal  artery,  or  ampulla.  These 
terminal  vessels  are  covered  by  a  lymphatic  sheath,  the  ellipsoidal 
sheaths.  The  terminal  ampullae  are  porous,  and  continue  as  veins. 
The  endothelial  cells  are  long  and  slender,  resembling  smooth  muscle 
cells,  and  are  contractile.  Their  edges  are  not  closely  approximated. 
In  the  splenic  vein  the  leukocytes  are  said  to  be  70  times  as  numerous 
as  in  the  splenic  artery. 

The  spleen  is  subject  to  rhythmic  contractions,  one  per  minute, 
and  about  18  per  cent,  of  its  volume  is  lost  at  each  contraction. 
These  are  produced  by  the  involuntary  muscle  in  the  capsule  and 
trabecular.  When  the  cardiac  impulse  sends  the  blood  into  the 
arteries,  the  blood  passes  into  the  ampullae,  and  through  the  porous 
walls  into  the  pulp  spaces.  When  the  rhythmic  contractions  occur, 
the  blood  is  forced  into  the  veins,  and,  at  the  same  time,  the  arteries 
are  closed.     This  shows  an  open  circulation  (Mall). 

The  lymphatics  are  trabecular  and  perivascular.  The  trabecular 
vessels  are  in  the  trabecular  and  in  the  capsule;  they  start  in  the  latter 
and  get  larger  toward  the  hilus.  The  perivascular  lymphatics  arise 
in  the  lymphoid  sheaths  of  the  arterioles  and  after  leaving  the  cor- 
puscles two  vessels  are  usually  formed  and  these  accompany  the 
artery  and  frequently  anastomose  around  it.  As  these  vessels  reach 
the  hilus  they  join  the  trabecular  vessels  and  the  efferents  from  the 
spleen  carry  the  lymph  to  the  splenic  nodes. 

The  nerves  are  chiefly  amyelinated  and  are  derived  from  the  solar 
plexus  of  the  sympathetic  system.     Plexuses  are  formed  around  the 


230  PRACTICAL  HISTOLOGY 

arteries  and  their  branches  and  fibers  pass  to  the  muscles  of  the 
vessels  and  the  smooth  muscle  of  the  capsule  and  trabecular. 

The  spleen  is  an  important  blood-cell-making  organ  throughout 
life.  In  fetal  life  it  is  an  important  center  for  the  production  of 
erythrocytes  but  by  birth  that  function  is  usually  lost.  In  certain 
blood  diseases  it  may  resume  that  function.  At  all  times  it  is  an 
important  center  for  the  formation  of  lymphocytes  and  some  of  the 
other  leukocytes,  though  in  lesser  quantities.  From  the  number  of 
disintegrating  red  cells  present  in  the  pulp  it  must  also  be  intimately 
concerned  with  the  destruction  of  the  useless  erythrocytes.  The 
hemoglobin  derived  from  these  cells  is  probably  utilized  by  the  liver 
in  the  manufacture  of  bilirubin  and  biliverdin. 

THYMUS  BODY 

The  thymus  body  is  essentially  a  lymphoid  structure,  though  it 
undergoes  peculiar  changes  in  its  life  history.  It  weighs  from  5  to 
1 1  grams  at  birth,  increases  in  size  and  weight  to  puberty  (40  to  50 
grams)  and  by  some  is  considered  active  until  the  fortieth  year, 
losing  its  function  after  that  time. 

It  originates  as  a  true  gland  (epithelial  organ),  but  soon  leukocytes 
enter  it,  and  cause  the  disappearance  of  the  epithelium  except  small 
islands.  After  the  sixth  year,  it  generally  undergoes  further  change 
or  involution.  The  lymphoid  tissue  is  gradually  replaced  by  adipose 
tissue,  so  that  an  old  thymus  will  show  but  little  lymphoid  tissue. 

This  organ  is  surrounded  by  a  capsule  of  white  fibrous  tissue  that 
sends  in  septa,  which  divide  the  organ  into  lobes  and  lobules. 
Within  the  lobule  there  is  a  delicate  reticulum  meshwork  for  the 
support  of  the  parenchyma  and  the  blood-vessels,  nerves  and  lym- 
phatics.    Each  lobule  consists  of  cortex  and  medulla. 

The  cortex  consists  of  dense  lymphoid  tissue  and  stains  deeply 
owing  to  the  large  number  of  leukocytes  present.  The  cortex  may 
be  subdivided  into  secondary  nodules  like  a  lymph  node,  by  trabec- 
ular septa  from  the  interlobular  connective  tissue.  Germinal  centers 
in  such  nodules  are,  however,  not  present. 

The  medulla  consists  of  diffuse  lymphoid  tissue,  and  takes,  there- 
fore, a  lighter  stain;  the  lymphoid  cells  are  chiefly  small  lymphocytes 


THE   LYMPHATIC   SYSTEM 


23I 


and  hyalin  cells  and  a  few  eosinophiles  and  giant  cells.  The  sup- 
portive tissue  is  reticulum,  which  is  coarser  than  in  the  cortex. 
Cortex  and  medulla  are  not  always  sharply  differentiated  from 
each  other.  At  times  band-like  extensions  of  the  medulla  may  pass 
from  one  lobule  to  the  other.     These  are  called  medullary  cords. 

In  the  medulla,  are  found  small,  peculiar  bodies,  consisting  of 
concentrically  arranged  epithelial  cells;  these  are  the  thymic  corpuscles, 
or  corpuscles  of  Has  sal.  These  are  at  first  12  to  20  microns  in  di- 
ameter and  increase  even  to  1 80  microns.     The  larger  ones  are  usually 


(C    ■ — 


Fig.  143. — Section-  of  the  Thymus  Body  of  a  Child. 
a.  Capsule;  b,  interlobular  connective  tissue;  c,  c,  adipose  tissue;  d,  blood-vessels 
in  interlobular  tissue;  e,  cortex;  /,  medulla;  g,  blood-vessel  in  lobule;  h,  h, 
corpuscles  of  Hassal;  i,  corpuscle  of  Hassal  magnified. 

compound.  New  ones  are  constantly  forming  from  the  reticular 
tissue.  The  nucleus  of  a  cell  disappears  and  hyalin  substance 
develops  in  the  cytoplasm.  The  peripheral  cells  are  usually  keratin- 
ized. The  center  may  calcify  or  fat  may  deposit.  The  formation 
of  these  bodies  is  considered  a  degenerative  process.  They  are  sup- 
posed to  represent  the  remains  of  the  epithelium,  though  some  hold 
that  they  represent  endothelium  of  blood-vessels.  These  bodies 
are  encapsulated,  and  may  be  compound. 

The  function  of  the  thymus  is  unknown.  It  is  a  center  for  the 
formation  of  lymphocytes  and  believed  by  some  to  give  rise  to  an 
internal  secretion  that  has  to  do  with  normal  growth  and  sexual 


232  PRACTICAL   HISTOLOGY 

development.  Its  change  from  epithelial  to  lymphoid  occurs  early 
in  fetal  life.  The  change  from  lymphoid  to  adipose  tissue  is  vari- 
able; although  its  involution  occurs  usually  from  the  sixth  year  to 
puberty  it  may  retain  its  essential  lymphoid  character  until  after 
middle  life  and  even  to  old  age.  Castration  delays  its  involution 
and  removal  of  the  thymus  in  young  animals  hastens  sexual  maturity, 
especially  in  the  male.  It  is  also  stated  that  its  removal  ultimately 
proves  fatal. 

The  numerous  arteries  pass  through  the  capsule  and  branch  in 
the  interlobular  connective  tissue.  From  these  vessels  branches 
pass  into  the  cortex  of  the  lobules  and  form  a  plexus  of  capillaries 
from  which  capillaries  proceed  to  the  medulla.  The  blood  is  col- 
lected into  venous  channels  that  pass  to  the  interlobular  connective 
tissue  where  they  join  to  form  larger  veins  that  ultimately  pass 
through  the  capsule  and  empty  into  the  left  innominate  vein. 

Small  lymphatic  vessels  are  found  in  the  medulla  and  cortex  of  the 
lobules.  These  communicate  with  larger  vessels  in  the  interlobular 
connective  tissue  in  which  these  vessels  anastomose  extensively. 
The  lymph  is  collected  into  one  or  two  vessels  for  each  lobe  and 
conducted  to  the  nearest  lymph  node. 

The  nerves  are  small  and  chiefly  sympathetic;  these  supply  the 
blood-vessels. 


CHAPTER  IX 

ALIMENTARY  TRACT 

The  alimentary  tract  -tarts  at  the  lips,  and  extends  to  the  anus 
It  receives  the  food,  digests  it  and  casts  off  that  which  is  undigested. 
The  various  portions  perform  different  functions,  and  the  lining  cells 
differ  accordingly.  The  inner  coat  is  a  mucous  membrane  that  gives 
rise  to  glands,  which  are  devices  of  nature  for  increasing  the  secretorv 
surface.  The  absorptive  surface  is  increased  by  prolongations  of  the 
mucosa  into  the  lumen  of  the  organ  (villi  of  the  small  intestine). 

The  lip  is  covered  externally  by  skin,  and  internally  by  mucous 
membrane.     Between  these,  are  found  connective  tissue  and  muscle. 

The  skin  consists  of  two  portions,  the  epithelial \  or  epidermis,  and 
the  connective  tissue  portion,  or  derma. 

The  epidermis  is  composed  of  stratified  squamous  cells,  of  which  two 
layers,  the  stratum  corneiim  and  stratum  Malpighii  are  distinct. 
The  stratum  corneum  is  the  outer,  and  consists  of  nonnucleated 
scales;  the  stratum  Malpighii  is  the  genetic  portion.  Its  lowest  cells 
rest  upon  a  basement  membrane,  and  are  columnar  in  shape.  Those 
above  are  polyhedral;  the  latter  become  more  flattened  as  the  corneum 
is  approached.  The  derma  consists  of  white  fibrous  connective 
tissue  supporting  blood-vessels,  nerves  and  lymphatics.  Beneath 
the  epithelium  it  is  thrown  into  projections  called  papillce. 

The  mucous  surface  is  also  lined  by  stratified  squamous  cells,  that 
differ  from  the  outer,  however,  in  being  larger  and  less  readily 
stained.  The  cells  rest  upon  a  basement  membrane,  beneath  which 
is  the  tunica  propria,  composed  of  papillated,  delicate  fibro-elastic 
tissue. 

Between  the  tunica  propria  and  skin,  are  found  connective  tissue 
and  voluntary  striated  muscle.  Xear  the  tunica  propria  are  to  be 
seen  small,  compound  tubular  glands  that  open  upon  the  mucous 
surface.     At  the  margin  of  the  lip  these  two  surfaces  join,  and  this 

233 


234 


PRACTICAL  HISTOLOGY 


is  the  mucocutaneous  junction',  here  the  epithelial  layer  is  quite  thick, 
and  the  cells  are  larger  and  bladder-like,  resembling  the  epitrichial 
cells  of  the  fetus. 

Blood-vessels  are  found  in  great  abundance,  and  form  dense  plex- 
uses, especially  around  the  glands. 

The  mouth  is  lined  by  a  mucous  membrane,  consisting  of  stratified 
squamous  cells  resting  upon  a  basement  membrane  and  tunica  pro- 


Fig.  144. — Section  of  the  Lip  of  a  Child  at  Birth. 
a,  Skin  surface;  b,  mucous  surface.     (Photograph.     Obj.  32  mm.;  oc.  5  x.) 

pria.  The  superficial  epithelial  cells  are  not  keratinized  and  the 
nuclei  may  be  distinct.  The  tunica  propria  consists  of  delicate 
areolar  tissue  that  supports  the  smaller  blood-vessels,  nerves  and 
lymphatics.  In  addition  diffuse  lymphoid  tissue  and  even  solitary 
nodules  are  met  with.  That  portion  next  to  the  basement  mem- 
brane is  thrown  into  delicate  projections  called  papillae;  as  a  result 
of  this  the  basal  epithelial  cells  have  a  very  uneven  course  and  the 
tunica  propria  is  referred  to  as  papillated. 

Small  salivary  glands  are  very  numerous  in  the  mucosa  and  even 
in  between  the  muscles;  these  are  named  according  to  the  region  in 


ALIMENTARY   TRACT  235 

which  they  are  found,  as  buccal  (cheek),  labial  (lips),  molar  (opposite 
the  molar  teeth  in  the  cheeks).  These  are  either  tubular,  or  tubulo- 
alveolar  in  structure.  The  tubular  glands  are  mostly  pure  mucous 
glands  while  the  mixed  glands  are  mixed  in  secretion  also.  The 
mucous  portion  of  the  glands  stains  lightly  with  the  ordinary 
plasmatic  stains  and  the  serous  acini  stain  deeply  under  the  same 
conditions.  They  are  readily  distinguished  from  each  other  under 
the  microscope.  Their  appearance  is  also  different  in  the  different 
stages  of  secretion  (rest  and  activity)  and  this  will  be  considered 
with  the  large  salivary  glands. 

The  gums  represent  that  portion  of  the  oral  mucosa  covering  the 
alveolar  processes  of  the  maxillae  and  mandible  and  the  necks  of  the 
teeth.  It  is  dark  red  in  color,  very  vascular  and  sensitive.  It  con- 
sists of  stratified  squamous  cells  resting  upon  a  basement  membrane 
that  is  very  thin  and  indistinct.  Beneath  this  is  the  tunica  propria 
that  consists  of  flattened  bundles  of  white  fibrous  tissue  that  are 
arranged  parallel  to  one  another;  these  fibers  are  arranged  in  three 
ways.  The  vertical  fibers  extend  from  the  basement  membrane  to 
the  periosteum;  the  horizontal  fibers  run  parallel  to  the  surface; 
the  radiate  fibers  are  arranged  fan-like  around  the  alveolar  margins 
and  include  fibers  derived  from  the  alveolodental  membrane.  Some 
elastic  fibers  are  present  between  the  bundles  of  white  fibrous  tissue 
which  are  quite  dense  and  almost  tendinous  and  with  the  fibers 
derived  from  the  periosteum  serve  to  bind  the  gum  firmly  to  the 
alveolar  periosteum. 

Over  the  palate  the  mucosa  consists  of  the  stratified  squamous 
cells,  basement  membrane  and  tunica  propria.  Over  the  front  of  the 
hard  palate  the  epithelial  layer  and  the  entire  mucosa  is  thinner  than 
over  the  back  portion;  the  tunica  propria  is  also  less  papillated  in 
front.  The  fibers  form  flat  bundles  that  make  a  denser  and  tougher 
layer  than  in  the  tunica  propria  in  general.  These  fibers  pass  from 
the  alveolar  borders  toward  the  center  of  the  palate  in  a  radiate 
manner  and  are  also  firmly  attached  to  the  periosteum. 

The  soft  palate  consists  of  a  double  layer  of  stratified  squamous 
cells,  continuous  at  the  free  edge  of  the  organ,  enclosing  between  them 
the  fibrous  aponeurosis  of  the  palate.  The  epithelial  cells  rest  upon 
the  thin  basement  membrane  beneath  which  is  the  tunica  propria 


236  PRACTICAL   HISTOLOGY 

consisting  of  a  network  of  white  fibrous  and  yellow  elastic  tissues. 
The  white  fibers  are  arranged  in  three  directions,  horizontally  (side 
to  side)  longitudinally  and  obliquely.  The  latter  fibers  extend  into 
and  blend  with  the  fibers  of  the  aponeurosis.  This  is  a  dense  layer 
of  white  fibrous  tissue  that  forms  the  center  of  the  soft  palate  and  it 
is  attached,  in  front,  to  the  periosteum  of  the  back  edge  of  the  hard 
palate  and,  behind,  it  extends  toward  the  free  edge  of  the  soft  palate 
and  forms  the  core  of  the  uvula.  The  tunica  propria  varies  in 
thickness  depending  upon  the  number  of  salivary  glands  present. 
These  glands  are  usually  small  and  of  the  mucous  variety.  The 
mucosa  is  thickest  at  the  free  edge  of  the  soft  palate.  The  phar- 
yngeal folds  have  the  same  general  structure  but  the  elastic  tissue 
is  more  abundant. 

Beneath  the  mucosa  of  the  oral  cavity  there  is  a  submucous  layer 
that  varies  in  thickness  in  different  regions.  It  serves  to  connect 
the  mucosa  to  the  underlying  structures  and  also  for  the  support  of 
vessels  and  glands.  On  the  gums  and  hard  palate  it  is  thin  and  rela- 
tively dense.  In  the  cheek  and  soft  palate  it  is  looser  and  compara- 
tively thicker  owing  to  the  salivary  glands  present. 

The  blood-vessels  are  quite  numerous  and  enter  the  submucous 
layer  from  which  arterioles  pass  to  the  mucosa  and  form  a  plexus  of 
capillaries  parallel  to  the  surface.  From  this  plexus  capillaries 
extend  into  the  papillae.  The  blood  is  collected  in  a  similar 
venous  plexus  and  returned  from  the  mucosa  in  a  corresponding 
manner. 

The  nerves  are  very  numerous  and  terminate  in  various  ways. 
The  vasomotor  nerves  are  sympathetic  and  pass  to  the  blood-vessels. 
The  sensor  nerves  are  myelinated  and  terminate  in  free  endings  or 
special  end  organs.  In  the  case  of  the  free  endings  the  nerve  fiber 
loses  its  sheaths  as  it  enters  the  epithelial  layer  and  the  naked  axis 
cylinder  then  divides  into  a  series  of  telodendrites  that  surround  the 
epithelial  cells  and  end  in  fine  granules,  or  end-discs.  Some  free 
endings  are  found  in  the  adventitia  of  the  blood-vessels.  The  organs 
are  corpuscles  of  Krause  and  are  found  in  the  papillae  of  the  tunica 
propria  and  are  similar  to  those  of  the  conjunctiva.  Other  sympa- 
thetic fibers  pass  to  the  epithelium  of  the  glands. 


ALIMENTARY    TRACT 


237 


consists,   anatomically,   of 

\ 


—  B 


THE  TEETH 

The  teeth  are  the  chief  organs  of  mastication  and  are  adapted  for 
cutting,  grinding,  holding,  etc.  Each 
crown,  that  portion  above  the  gum;  root 
or  fang,  that  portion  in  the  jaw;  neck, 
the  narrow  portion  between  the  pre- 
ceding, covered  by  the  gum. 

Histologically  considered,  there  are 
the  enamel  that  covers  the  crown;  the 
dentin  that  forms  the  bulk  and  gives 
the  shape  of  the  tooth;  the  cementum 
that  covers  the  dentin  of  the  fang;  the 
peridental  membrane  that  surrounds 
the  root  and  holds  the  tooth  in  place; 
the  pulp  that  occupies  the  pulp  cavity 
and  is  the  nutritive  and  sensitive  por- 
tion of  the  organ.  In  the  root  of  the 
tooth  is  a  canal  that  leads  into  the  pulp 
chamber;  this  is  the  root  canal. 

The  enamel  is  the  hardest  substance 
in  the  body  and  forms  a  cap-like  cover- 
ing, of  varying  thickness,  of  the  dentin. 
It  is  thickest  at  the  cutting  or  occlusal 
surface  of  the  teeth  and  diminishes  in 
thickness  as  the  neck  is  approached. 
It  is  said  to  consist  of  97  per  cent.,  or 
more,  of  inorganic  matter  and  3  per 
cent.,  or  less,  of  organic  matter.  Bibra 
gives  the  composition  as  follows: 
Earthy  material  96.6  per  cent.;  animal 
material  3.5  per  cent.  The  former 
includes  phosphate  of  calcium  (with 
traces  of  calcium  fluorid)  89.8  per  cent.; 
calcium  carbonate  4.4  per  cent.;  mag- 
nesium phosphate,  etc.,  1.3  per  cent. 
Berzelius  found  only  2  per  cent,  of 
animal  material   and   8  per  cent,  of  calcium  carbonate. 


Fig.  145. — Longitudinal  Sec- 
tion of  an  Incisor  Tooth. 

A,  Crown;  B,  neck;  C,  fang; 
I,  enamel;  2,  dentin;  3,  pulp 
cavity;  4,  cementum;  5,  root- 
canal.  {After  Stohr's 
Histology.) 


238 


PRACTICAL  HISTOLOGY 


The  enamel  consists  of  hexagonal  enamel  prisms  that  are  arranged 
perpendicular  to  the  surface  of  the  dentin,  and  represent  modified  epi- 
thelial cells.  The  surface  of  the  enamel  is  marked  by  delicate  stria- 
tions  which  indicate  the  enamel  prisms.  Each  enamel  prism  or  fiber 
is  about  5  microns  in  diameter,  has  a  wavy  or  tortuous  course  with 
its  inner  end  fitting  into  a  slight  depression  in  the  dentin.  The  prism 
is  of  the  same  diameter  throughout,  though  the  sides  may  not  be 


Enamel  rods 

fully  in 

transverse 

section 


Enamel  rods 

variously 

distributed 


Enamel  rods 
not  fully  in 
transverse 
section 


Enamel  rods 
of  irregular 
form 


]Fig.  146. — Human    Enamel.     Transverse    ground    sections.     (Broomell    and 

Fischelis,  after  Gysi.) 


straight  and  even.  They  are  arranged  in  bundles  in  which  the 
constituent  prisms  are  parallel  to  one  another.  The  various  bundles 
are  not  always  parallel  to  one  another.  As  a  result,  near  the  surface 
of  the  tooth  shorter  additional  prisms  are  found  and  these  are  the 
supplemental  prisms.  The  prisms  seem  to  be  held  together  by  a 
transparent  cement  which  is  apparently  inorganic  in  composition. 
In  a  prepared  section  of  the  tooth  are  seen  some  brown  strialions  that 


ALIMENTARY  TRACT  239 

run  almost  parallel  to  the  surface  of  enamel  or  dentin  and  in  the 
latter  instance  may  run  the  entire  extent  of  the  crown.  These  are  the 
"  brown  striae  of  Retzius."  The  cause  of  these  striae  is  still  in  dispute. 
Tomes  believes  that  they  represent  successive  positions  of  the  enamel 
cap.  Minute  fissures  may  exist  between  the  enamel  bundles  in  the 
deeper  portions  of  the  enamel.  At  times  large  fissures  are  found 
that  extend  downward  from  the  depressions  between  the  cusps  of 
the  molar  teeth. 

When  studied  with  reflected  light  the  "radial  lines  or  prism  stripes 
of  Schreger"  are  seen  in  the  enamel.  These  are  apparently  due  to 
various  directions  taken  by  the  different  bundles  of  enamel  prisms, 
and  are  well  marked  near  the  surface  of  the  dentin  and  less  so  toward 
the  surface  of  the  enamel.  The  enamel  prisms  are  best  studied  in 
the  newly  formed  or  still  growing  teeth.  When  these  are  subjected 
to  the  action  of  acids  the  enamel  prisms  are  readily  dissociated  or 
broken  up. 

Dentin. — This  portion  forms  the  bulk  of  the  tooth  and  gives  it  its 
shape.  It  is  yellowish-white  in  color,  harder  than  bone,  and  repre- 
sents ivory.  It  is  everywhere  covered  by  either  enamel  or  cemen- 
tum.  It  is  composed  of  about  72  per  cent,  of  inorganic  matter  and 
of  about  28  per  cent,  of  organic  matter. 

The  parts  of  importance  are  the  dentinal  sheaths,  matrix,  and 
dentinal  fibers.  The  dentinal  sheaths,  or  Neumann's  sheaths,  are 
delicate  tube-like  masses  of  dense  dentin  that  seem  indestructible 
and  will  persist  when  the  matrix  has  been  destroyed.  They  extend 
in  a  curved  or  spiral  course  from  the  pulp  cavity  to  the  enamel  or 
cementum,  diminishing  in  diameter  as  they  pass  outward.  Within 
the  sheaths  are  spaces  called  dentinal  tubules,  or  canaliculi.  They 
radiate  from  the  pulp  cavity  to  the  periphery  and  have  the  same 
curved  or  spiral  course  of  the  sheaths.  They  diminish  in  diameter 
from  within  outward,  and  terminate  at  the  enamel  or  cemental 
surface  either  by  anastomosing  with  one  another,  ending  bluntly  or 
opening  into  the  interglobular  spaces.  Some  are  said  to  penetrate 
into  the  enamel  and  cementum;  in  the  latter  they  communicate 
with  the  canaliculi.  The  pulp  cavity  end  is  usually  funnel-shaped 
(5.5  microns),  and  the  tubules  here  are  closely  packed  so  that  there  is 
very  little  matrix.     The  tubules  are  from  2  to  4  microns  in  diameter 


240 


PRACTICAL   HISTOLOGY 


at  the  beginning  and  0.5  to  1  micron  at  the  peripheral  end.  The 
tubules  branch  toward  the  enamel  or  cementum;  the  branches  are 
most  numerous  in  the  fang.  These  tubules  may  show  constrictions 
at  intervals.  The  curvatures  of  the  tubules  are  long  and  short,  or 
primary  and  secondary,  respectively.  As  these  occur  regularly  they 
produce  the  incremental  lines  of  Schreger.  These  are  lines  that 
are  parallel  to  the  surface  of  the  dentin. 


Enamel 


Dentin 


Fig.   147.— Comparison   in   the   Appearance   of   the   Enamel  and   Dentin 
under  Low  Power  of  the  Microscope.      x  40.     (Broomell  and  Fischelis.) 


The  dentinal  fibers,  or  Tome's  fibers,  represent  the  processes 
of  the  odontoblasts  and  they  occupy  the  dental  tubules,  branching 
as  the  latter  do  and  diminishing  in  size  as  the  tubules  become  smaller. 
Some  claim  that  they  do  not  belong  to  the  odontoblasts,  but  repre- 
sent nerve  tissue  surrounded  by  connective  tissue. 

The  matrix  occupies  the  space  between  the  dentinal  sheaths.  It 
consists  of  a  more  or  less  homogeneous  dentin  that  is  not  so  hard 
as  that  surrounding  the  canaliculi  in  the  form  of  the  dentinal  sheaths. 


ALIMENTARY    TRACT 


241 


Upon  decalcification  it  can  be  separated  into  lamellae  parallel  to  the 
pulp  surface.  Fibers  are  also  said  to  be  present.  It  is  less  abundant 
near  the  pulp  cavity,  as  the  sheaths  here  are  very  close  together. 
Farther  out,  as  the  sheaths  become  smaller  in  diameter,  the  matrix 
increases  and  along  the  margin  of  the  dentin  near  the  enamel,  a  vary- 
ing number  of  small  irregular  spaces,  the  interglobular  spaces,  are  seen; 
these  represent  areas  of  imperfect  calcification  and  they  are  filled 


Gementum 


V, 


Dentin 


m  % 

if'* 

\, 

' 

'y 

> 

Fig.  148. — Transverse  Section  Through  the  Root  of  a  Human  Incisor 
Showing  the  Dentin  Surrounded  by  the  Cementum.  X  30.  (Broomell 
and  Fischelis.) 


with  a  gelatinous  substance.  Between  dentin  and  cementum  these 
spaces  are  smaller,  and  under  1owt  power  give  a  granular  appearance 
to  the  area;  this  represents  "Tome's  granular  layer." 

Osteodentin  may  be  deposited  in  the  pulp  cavity.  This  resembles 
bone  and  contains  pulp  and  vessels.  The  dentinal  substance  may 
be  arranged  like  an  Haversian  system  and  numerous  tubules  may 
radiate  from  the  central  canal. 

Repair  dentin  may  be  formed  in  the  pulp  cavity,  opposite  to  an 
injury  upon  the  surface  of  the  tooth  (crown  or  neck).     The  dentinal 


16 


242 


PRACTICAL  HISTOLOGY 


tubules  here  are  then  blocked  and  if  the  injury  be  extensive  the 
repair  dentin  may  fill  the  pulp  cavity. 

Cementum. — The  crusta  petrosa  is  a  bone-like  substance  that 
covers  the  root  of  the  tooth.  It  consists  of  about  66  per  cent,  inor- 
ganic matter  and  34  per  cent,  organic  matter.  It  is  thickest  at  the 
apex  of  the  tooth  and  becomes  gradually  thinner  as  the  cervix  or 
neck  is  approached  and  ends  at  the  lower  margin  of  the  enamel. 


W 


Alveolar  wall 


Cementum 


Alveolo- 

dental 

membrane 


V 


* 


Dentin 


31ood  vessels  of 

alveolodental 

membrane  in 

^transverse 

section 


Fig.  149. — Transverse  Section  through  Root  of  Human  Incisor  and  Sur- 
rounding Alveolar  Wall,  with  Alveolodental  Membrane  Interven- 
ing.      X  40.      (Broomell  and  Fischelis.) 


It  resembles  bone  very  closely,  contains  lacunae,  canaliculi  and 
lamellae.  According  to  Schafer  Haversian  systems  are  at  times 
found  where  the  cementum  is  thick.  The  lamellae  are  about  the 
same  in  number  but  thicker  at  the  apex  than  near  the  cervix.  This 
applies  to  young  teeth.  In  older  teeth  the  layers  are  not  only 
much  thicker  near  the  apex  but  are  also  more  numerous,  the  shorter 
added  lamellae  constituting  supplemental  lamellae.  The  layers  may 
or  may  not  run  parallel  to  the  dentin.     Passing  through  the  lamellae 


ALIMENTARY  TRACT  243 

at  varying  intervals  are  fibers  of  Sharpey.  Between  the  lamella; 
are  irregular  spider-like  lacuna  that  vary  in  size  but  resemble  in 
shape  and  number  of  canaliculi,  those  of  bone;  they  lie  partially  in 
one  layer  and  partially  in  another  and  their  long  axes  are  parallel 
to  the  surface  of  the  tooth.  Extending  out  from  the  lacunae  are 
the  canaliculi  which  usually  are  directed  peripherally,  though  some 
are  seen  extending  in  all  directions. 

The  cementoblasts  occupy  the  lacunae.  They  are  oval,  stellate, 
or  elongated  elements  and  usually  correspond  in  direction  to  the 
lacunae.  The  processes  vary  in  length  and  form,  and  most  of  them 
extend  toward  the  periphery,  following  the  canaliculi. 

Dental  Pulp. — The  pulp  is  the  highly  vascular  and  sensitive 
mucous  connective  tissue  that  occupies  the  pulp  cavity,  or  chamber 
and  root  canals  and  is  concerned  with  the  nutrition  and  growth 
of  the  tooth.  It  is  composed  of  cells  and  intercellular  substance 
and  contains  blood-vessels  and  nerves. 

The  cells  are  of  various  varieties,  the  most  important  of  which  are 
the  odontoblasts.  These  cells  are  found  upon  the  surface  of  the 
pulp  and  form  a  continuous  layer  of  cells  one  layer  deep.  They 
are  elongated  flask-shaped  elements,  about  40  microns  in  height, 
from  which  three  sets  of  processes  extend.  These  are  dentinal, 
pulpal  and  lateral.  The  dentinal  process,  or  processes,  arise  from  the 
peripheral  end  of  the  cell  and  extend  into  the  dentinal  tubules,  and 
they  have  been  described  under  the  dentin.  The  lateral  processes 
pass  from  the  sides  of  the  cells  to  the  neighboring  cells,  while  the 
pulpal  processes  extend  from  the  central  ends  of  the  odontoblasts 
to  the  deeper  cellular  elements  of  the  pulp.  The  nucleus  occupies 
the  end  of  the  cell  next  the  pulp  reticulum.  Beneath  the  layer  of 
odontoblasts  there  is  a  narrow  layer  of  tissue  almost  devoid  of  cells, 
then  an  area  of  which  the  cells  are  quite  numerous,  and  again  a 
region,  the  center  of  the  pulp,  in  which  there  are  very  few  cellular 
elements.  The  cells  are  spindle-shaped,  stellate  and  spheroid  in 
form  and  possess  many  or  few  hair-like  processes  that  pass  in  all 
directions. 

The  arteries,  apical,  of  the  pulp  are  derived  from  a  branch  that 
enters  the  root  canal  of  the  tooth;  as  this  vessel  passes  toward  the 
pulp  chamber  it  gives  off  branches  that  form  plexuses  parallel  to 


244  PRACTICAL  HISTOLOGY 

the  long  axis  of  the  tooth;  ultimately  forming  rich  capillary  plexuses 
in  the  neighborhood  of  the  odontoblastic  layer.  The  blood  is  col- 
lected by  venous  channels  that  anastomose  freely  and  empty  into 
one  channel  that  leaves  through  the  root  canal. 

The  nerves,  one  or  more,  pass  through  the  root  canal  giving  off 
a  few  fibers  here;  in  the  pulp  chamber  branches  are  distributed  in 
every  direction  forming  arch  plexuses,  after  losing  their  myelin 
sheaths,  beneath  the  layer  of  odontoblasts.  From  this  plexus  fibers 
are  said  to  pass  between  the  odontoblasts  to  end  in  bulbous  enlarge- 
ments within  the  central  ends  of  the  dentinal  tubules.  Magitot 
claims,  however,  that  the  dentinal  fibers  are  continuations  of  the 
nerve  fibers.  Mummery  states  that  two  nerve  fibers  from  the  plexus 
around  the  odontoblasts  enter  each  tubule  and  this  accounts  for 
the  extreme  sensitiveness  of  the  dentin.  Sympathetic  motor  fibers 
supply  the  muscle  tissue  of  the  pulp  vessels. 

The  peridental,  or  alveolodental  membrane,  is  a  highly  vascular 
and  sensitive  white  fibrous  tissue  membrane  that  lines  the  alveolar 
processes  of  the  jaw  and  covers  the  roots  of  the  teeth.  It  is  thickest 
at  gum  and  apical  portions  and  thinnest  in  the  middle.  The  fibrous 
elements  are  bundles  of  white  fibrous  tissue  that  pass  into  the 
cemental  layers  on  the  one  hand  and  into  the  bony  tissue  of  the  jaw 
on  the  other  hand,  resembling  Sharpey's  fibers.  In  general,  around 
the  apex  of  the  tooth  the  fiber  bundles  are  arranged  fan-like  and  are 
directed  upward  and  outward.  In  the  body  of  the  tooth  the  fiber 
bundles  pass  directly  outward  from  the  cementum  to  the  alveolar 
wall  and  are  largest  and  strongest  here.  At  the  gum  margin  the 
fiber  bundles  pass  outward  and  are  lost  in  the  fibrous  tissue  of  the 
gum,  or  pass  toward  the  adjacent  tooth  as  the  case  may  be. 

Upon  the  inner  surface  of  the  membrane  are  found  the  cement  oblasts; 
these  are  irregular  flattened  elements  possessing  a  clearly  defined 
nucleus  and  numerous  delicate  irregular  processes  that  extend  in 
various  directions.  They  are  evenly  distributed.  Upon  the  oppo- 
site (alveolar)  surface  of  this  membrane  are  the  osteoblasts  that  form 
the  bone  of  the  jaw.  In  the  meshes  of  the  fiber  bundles  are  found 
fibroblasts  or  connective-tissue  cells  and  some  osteoclasts  or  bone- 
destroying  cells.  The  latter  are  large,  fairly  regular,  oval  or  round 
cells  that  possess  several  nuclei  and  usually  have  no  processes. 


ALIMENTARY   TRACT  245 

The  arteries  are  derived  from  the  apical  artery  and  pass  up  parallel 
to  the  long  axis  of  the  tooth,  giving  off  branches  at  intervals,  these 
form  capillary  plexuses  beneath  the  alveolar  and  cemental  side  of 
the  membrane.  The  blood  is  collected  by  venous  channels  that 
ultimately  empty  into  the  apical  vein. 

The  veins  are  tributary  to  those  at  the  apex  and  are  distributed 
somewhat  like  the  arteries. 

The  functions  of  the  alveolodental  membrane  are  physical  and 
sensor.  It  holds  the  tooth  in  place,  returns  it  to  its  normal  position 
when  slightly  rotated  or  displaced;  upon  one  side  it  forms  cementum 
and  upon  the  other  it  forms  bone. 

Nasmyth's  Membrane. — This  enamel  cuticle  is  a  thin  indestructi- 
ble membrane  covering  the  enamel  of  the  unworn  tooth.  It  is  said 
by  some  to  be  the  remains  of  the  enamel  organ,  while  others  claim 
it  is  a  continuation  of  the  cementum.  The  former  seems  the  more 
probable  origin.  It  forms  a  protective  covering  and  is  horny  in 
nature.  It  resists  the  action  of  strong  acids  and  also  prolonged 
boiling.  With  silver  nitrate  outlines  like  those  of  pavement  epithe- 
lium are  produced.  It  is  made  up  of  short,  uncalcified  prisms  that 
are  flattened  in  shape  and  represent  the  last  formed  portions  of  the 
enamel  prisms  before  calcification  takes  place. 

THE  TONGUE 

The  tongue,  like  the  teeth,  occupies  part  of  the  mouth  cavity. 
It  is  covered  by  a  mucous  membrane  that  consists  of  stratified 
squamous  cells,  basement  membrane  and  tunica  propria,  which,  along 
the  sides  and  base,  is  papillated.  The  superficial  surface  of  the 
epithelium  of  the  sides  and  under  surface  of  the  tongue  is  regular 
and  even  in  its  course  and  the  tunica  propria  is  thick  throughout. 
The  upper  surface,  or  dorsum,  is  characteristic.  It  is  continuous 
with  the  mucosa  lining  the  oral  cavity.  Its  apical  two-thirds  is 
covered  by  minute  projections,  called  papillce;  of  these  there  are 
three  varieties,  filiform,  fungiform  and  vallate.  The  central  portion 
consists  chiefly  of  voluntary  striated  muscle  that  forms  the  bulk 
of  the  organ. 

The  filiform  papillae  are  cone-shaped  projections  of  the  tunic a  propria, 
covered  by  the  stratified  squamous  cells,  the  outer  ones  of  which  are 


246 


PRACTICAL  HISTOLOGY 


hard  and  horny.  They  vary  in  height  from  0.5  to  2.5  mm.  The 
central  part  of  a  papillae  consists  of  white  fibrous  tissue,  which  is 
thrown  into  small  secondary  papilla  that  are  not  visible  externally. 
These  papillae  are  the  most  numerous,  and  are  scattered  over  the 
whole  of  the  apical  two-thirds.  They  are  directed  backward,  and 
are  the  ones  that  produce  the  scratching  sensation  when  the  hand 
is  licked  by  a  lower  animal.  In  these  animals  these  papillae  are 
very  long  and  the  amount  of  keratinized  epithelium  is  great. 


Primary 
papilla. 


Secondary 
papillae. 


Filiform  process. 


Fat  cells.  Fascia  linguae.  Muscle. 

Fig.  150. — From   a  Longitudinal  Section  of  the   Dorsum  of  a   Human 
Tongue.      X  12.     {Lewis  and  Siohr.) 


The  fungiform  papillae  are  flat-topped,  table-like  structures,  in 
which  the  sides  are  parallel.  They  have  secondary  papillae,  and 
are  scattered  like  the  filiform  variety,  but  are  less  numerous.  Each 
consists  of  a  large  central  core  of  tunica  propria  that  usually  has 
secondary  papillae.  In  the  stratified  squamous  cells  covering  these 
papillae  taste-buds  are  occasionally  found.  They  are  usually  not 
over  1.5  mm.  high. 

The  vallate  papillae  are  the  most  important.  While  the  top  is 
flat,  the  sides  usually  converge  and  give  this  variety  a  narrow  base. 
Secondary  papillce  are  found  only  on  the  upper  portion.  Each  papilla 
is  surrounded  by  a  little  vallum,  or  ditch,  hence  the  name;  this  is 


ALIMENTARY   TRACT 


247 


due  to  the  fact  that  these  papillae  are  beneath  the  general  surface 
level  of  the  mucosa  of  the  tongue. 

These  papillae  are  the  least  numerous,  and  are  found  only  in  one 
area.  Ten  to  fifteen  arrange  themselves  like  a  letter  V,  with  the 
apex  at  the  foramen  cecum,  a  little  depression  that  lies  at  the  bound- 
ary of  the  apical  two-thirds  and  basal  one-third  of  the  tongue. 
These  papillae  contain  taste-buds  along  their  sides. 


mk 


Fig.  151. — Section  of  a  Taste-bud  of  a  Rabbit. 

e,  Epithelium;  p,  taste   pore    with    gustatory    hairs;  s,  sustentacular    cells;  t, 
gustatory  cells;  ft,  nerve  fibers.     {After  Ranvier.) 

The  taste-buds  are  the  organs  of  taste  and  lie  in  the  epithelial 
layer  of  the  vallate  papillae  as  well  as  in  the  epithelial  layer  of  some 
of  the  fungiform  papillae,  in  the  epithelium  of  the  soft  palate,  uvula, 
papillae  foliatae  and  the  ventral  surface  of  the  epiglottis.  They  are 
ovoid  or  barrel-shaped  structures.  The  superficial  extremity  is 
narrow  and  extends  nearly  to  the  surface  of  the  epithelial  layer; 
the  deeper  part  is  broader  and  rests  upon  the  basement  membrane. 
At  the  superficial  end  there  is  a  small  opening  called  the  gustatory 
pore,  that  leads  through  a  short  canal  to  the  surface  of  the  papilla. 


248 


PRACTICAL   HISTOLOGY 


Each  bud  consists  of  two  kinds  of  cells,  the  outer,  stave-like  ele- 
ments called  the  sustentacula^  cells;  the  inner,  neuroepithelial  cells. 

The  sus tentacular,  or  supporting  cells,  are  elongated  elements  the 
outer  ends  of  which  are  pointed  and  form  the  boundary  of  the  taste- 
pore.     The  basal  extremities  of  these  cells,  are  broad  and  irregular 

I  and  rest  upon  the  basal  cells,  to  which 
they  may  be  connected  by  protoplasmic 
processes. 

The  gustatory  cells  are  of  the  neuroepithe- 
lial type.  They  are  so  thin  that  the  nucleus 
forms  a  large  bulge  near  the  center  of  each 
cell.  The  basal  extremity  of  each  cell  is 
usually  branched  and  connected  to  the 
basal  cells  by  delicate  protoplasmic  proc- 
esses. The  outer  extremity  is  continued 
as  delicate  hair-like  process  that  extends 
into  the  epithelial  canal  beyond  the  taste- 
pore  and  almost  to  the  surface  of  the  epi- 
thelium of  the  mucosa  of  the  papilla.  The 
finely  granular  cytoplasm  contains  a  deeply 
staining,  rod-shaped  nucleus. 

The  basal  cells  are  flattened  elements 
that  lie  at  the  base  of  the  taste-bud.  The 
cytoplasm  is  small  in  amount  and  extends 
as  many  processes  that  connect  with  the 
other  cells  of  the  taste-bud.  The  nucleus 
contain  but  little  chromatin.  These  cells 
are  supposed  to  be  supportive  in  function. 
The  nerve  fibers  arise  from  the  subepithelial  plexus  of  nerve  fibers. 
These  terminal  fibers  end  in  three  ways.  Some  enter  the  organ 
(intragemmal)  where  they  divide  into  fibrils  that  are  varicose  and 
end  in  small  knobs  between  the  neuroepithelial  cells.  Others 
surround  the  taste-bud  (circiimgcmmal)  and  the  fibrils  terminate 
upon  the  sustentacular  cells.  Others  end  between  the  neighboring 
epithelial  cells  of  the  mucosa  {inter gemmed). 

Beneath  the  mucosa  is  found   the  musculature  of  the  tongue. 
This   consists  of   the   voluntary  striated   variety,   arranged   longi- 


Fig.  152. — Golgi  Prepara- 
tion of  the  Nerve 
Fibers  of  a  Test-bud. 
Intragemmal  fibers;  i,  i, 
intergemmal  fibers;  c, 
circumgemmal  fibers;  n, 
nerve  fibers.  {After 
Retzius.) 


a, 


ALIMENTARY   TRACT 


249 


Fig.  153. — Cross-section  of  Tongue. 

a,  Stratified  squamous  cells;  b,  basement  membrane;  c,  tunica  propria;  d,  serous 
glands;  e,  mucous  glands;/,  venule;  g,  longitudinal  muscle  fibers;  h,  vertical 
muscle  fibers;  *,  transverse  muscle  fibers;  I,  septum;  m,  filiform  papilla; 
n,  secondary  papillae;  r,  adipose  tissue.  A,  Filiform  papilla.  B,  Fungi- 
form papilla.  C,  D,  Circumvallate  papillae — m,  m,  taste-buds;  n,  n,  glands. 
E,  Taste-bud — 0,  nucleus  of  neuro-epithelial  cell;  r,  nerve  fiber;  s,  gustatory 
hair;  t,  sustentacular  cell;  v,  neuro-epithelial  cell. 


250  PRACTICAL  HISTOLOGY 

tudinally,  vertically  and  transversely.  The  longitudinal  fibers  are 
arranged  in  bundles  that  lie  beneath  the  tunica  propria  and  extend 
around  the  tongue.  They  are  separated  by  small  bundles  of  vertical 
fibers.  In  the  center,  the  fibers  are  vertical,  oblique  and  transverse, 
and  are  separated  in  the  middle  fine  by  a  little  partition,  or  septum. 
This  consists  of  white  fibrous  tissue,  and  arises  at  the  base,  but  does 
not  reach  the  tip.  It  varies  in  height,  being  higher  in  the  middle 
than  at  either  end.  In  the  muscular  portion,  small  salivary  glands 
are  often  found.     Occasionally,  branched  muscle  fibers  are  found. 

The  mucosa  of  the  true  base  of  the  tongue,  basal  one-third,  pos- 
sesses no  papillae.  The  epithelial  surface,  however,  is  not  smooth 
and  regular  but  presents  a  large  number  of  little  rounded  elevations 
each  of  which  shows  a  small  central  opening.  These  elevations 
indicate  the  presence  of  the  lingual  tonsils  and  the  openings  are  the 
orifices  of  the  crypts. 

The  epithelium  is  of  the  stratified  squamous  variety  and  these 
cells  rest  upon  a  thin  basement  membrane  and  a  rather  thick  tunica 
propria  that  consists  of  areolar  tissue.  The  crypts  are  tubular 
extensions  of  the  epithelium  of  the  surface  of  the  tongue  and  these 
epithelial  cells  are  the  lining  cells  of  these  tonsillar  crypts.  In  the 
tunica  propria  surrounding  each  crypt  there  is  a  solitary  nodule. 
It  is  this  nodule  of  lymphoid  tissue  that  bulges  the  epithelium  and 
forms  the  rounded  elevations  upon  the  surface.  Lymphocytes 
pass  through  the  epithelial  layer  and  enter  the  crypts  of  the  lingual 
tonsils.  The  basal  one-third  of  the  tongue  represents  an  extensive, 
widespread  but  shallow  tonsil,  a  part  of  the  tonsillar  ring  surrounding 
the  pharyngeal  orifice. 

Minute  salivary  glands  are  very  numerous  in  the  tongue  and  are 
called  lingual  glands.  These  are  usually  buried  in  between  the  mus- 
cle bundles  and  their  ducts  pass  to  all  surfaces.  Upon  the  ventral 
(under)  surface  near  the  tip,  under  the  mucosa,  are  two  of  the  largest 
glands  and  these  are  called  the  apical  glands.  The  glands  are  espe- 
cially numerous  at  the  root  of  the  tongue.  These  glands  are  of  both 
the  mucous  and  serous  types. 

The  tongue  is  very  vascular  and  is  supplied  by  the  lingual  artery 
chiefly.  This  artery  and  vein  are  deeply  buried  and  from  the  artery 
branches  pass  to  the  deeper  parts  of  the  tunica  propria  and  form  a 


ALIMENTARY  TRACT 


251 


plexus  of  vessels.  From  this  plexus  of  capillaries  others  are  given 
off  that  pass  to  the  superficial  portions  of  the  tunica  propria  and  in 
the  papillae  form  loops  that  are  characteristic.  From  the  deeper 
side  of  the  plexus  vessels  supply  the  musculature  and  glands.  The 
blood  is  returned  by  venous  channels  that  have  a  corresponding  course. 
The  lymphatics  are  superficial  and  deep.  The  former  start  in  the 
intercellular  spaces  beneath  the  epithelium;  around   the  lingual 


Fig.  154. — Cross-section  of  an  Injected  Tongue. 
Note  the  abundant  vessels  in  the  papillae.     (Photograph.     Obj.  32  mm.) 

tonsils  these  lymphatics  are  very  numerous  and  the  capillaries  form 
plexuses  around  the  nodules.  The  deep  set  is  located  near  the  surface 
of  the  musculature  and  receives  the  lymph  from  the  superficial  set 
and  also  from  the  deep  structures  of  the  tongue.  The  efferents  from 
this  plexus  carry  the  lymph  to  the  lingual  and  deep  cervical  lymph 
nodes. 

The^nerves  are  from  the  cerebrospinal  and  sympathetic  systems. 
The  cerebrospinal  nerves  are  sensor  and  motor.  The  sensor  are  for 
general  sensibility  and  special  sense  of  taste.     The  former  terminate 


252  PRACTICAL   HISTOLOGY 

in  free  endings  in  the  tunica  propria  of  the  papillae  and  the  deeper 
connective  tissue;  some  terminate  in  muscle  spindles.  The  nerves 
of  special  sense  of  taste  pass  in  small  bundles  of  fibers  to  the  bases 
of  the  papillae  containing  the  taste-buds.  These  form  a  plexus 
beneath  the  epithelial  cells  and  from  this  plexus  fibers  are  dis- 
tributed to  the  interior  of  the  taste-buds,  to  the  surface  of  the  taste- 
buds  and  to  the  surrounding  epithelium.  In  the  latter  instance 
the  naked  fibers  end  between  the  epithelial  cells. 

THE  TONSILS 

The  palatal  tonsils  are  located  at  the  beginning  of  the  pharynx  one 
on  each  side  of  the  base  of  the  tongue,  between  the  glossopalatal  and 
glassopharyngeal  folds.  They  are  essentially  lymphoid  in  structure 
but  being  so  intimately  related  with  the  alimentary  tract  they  will 
be  described  here.  Each  is  about  2  to  2.5  cm.  long,  18  mm.  wide 
and  12  to  15  mm.  thick. 

Upon  its  pharyngeal  surface  each  is  covered  by  a  continuation  of 
the  mucosa  of  the  oral  cavity.  This  consists  of  stratified  squamous 
cells  that  rest  upon  a  thin  basement  membrane  beneath  which  is  the 
tunica  propria  consisting  of  areolar  tissue.  Laterally  the  organ  is 
surrounded  by  a  capsule  of  rather  dense  white  fibrous  tissue  that 
separates  it  from  the  surrounding  tissues.  This  capsule  sends  in 
trabecular  that  form  the  gross  framework  of  the  organs;  within  this 
there  is  a  delicate  meshwork  of  reticulum  that  supports  the  function- 
ating cells,  small  blood-vessels,  nerves,  and  lymphatics.  In  the  trabe- 
cular are  found  the  larger  vessels  and  nerves.  Upon  the  pharyn- 
geal surface  of  the  organ  are  noted  a  number  of  openings  that  are  the 
orifices  of  the  tonsillar  crypts.  These  crypts  are  usually  long 
and  tortuous  and  those  of  the  upper  portion  of  the  structure  are 
said  to  pass  downward  and  laterally.  These  crypts  are  lined  with 
stratified  squamous  cells  continued  from  the  pharyngeal  surface,  and 
in  this  epithelial  layer  are  seen  varying  numbers  of  leukocytes  called 
salivary  corpuscles.  These  are  ameboid  leukocytes  that  wander 
through  the  epithelium  into  the  crypts.  When  examined  fresh  the 
granules  of  the  cells  may  exhibit  Brownian  motion.  The  epithelium 
in  areas  may  often  show  degenerative  changes. 


ALIMENTARY    TRACT 


253 


Within  the  reticulum  is  seen  the  parenchyma  that  is  composed  of 
lymphoid  tissue  of  the  diffuse  and  solitary  nodule  varieties.  The 
cells  are  chiefly  small  and  large  lymphocytes.  The  solitary  nodules 
all  show  germinal  centers  and  these  structures  are  arranged  in  a  single 
row  around  the  crypts;  the  remainder  of  the  intercrypt  reticulum  is 
filled  with  the  diffuse  lymphoid  tissue  which  will  also  fill  in  such 
spaces  as  are  not  occupied  by  the  solitary  nodules.  The  ducts  of 
small  mucous  glands  are  said  to  empty  into  the  crypts  at  times. 


BRUHi  atm 


rtV-3  Cfflv>.   ■  •   r-:  1 


®ri* 


Fig.  155. — Vertical  Section  of  a  Human  Palatal  Tonsil. 

a,  Stratified  epithelium;  b,  basement  membrane;  c,  tunica  propria;  d,  trabecular; 
e,  diffuse  lymphoid  tissue;  /,  nodules;  h,  capsule;  i,  mucous  glands;  k,  striated 
muscle;   /,  blood  vessel;  q,  pits. 


Under  the  palatoglossal  fold  there  seems  to  be  an  area  that  corre- 
sponds to  a  hilus  as  the  larger  vessels  seem  to  enter  here.  Other 
arterial  vessels  enter  at  different  points  on  the  capsule.  These 
vessels  all  branch  and  the  larger  divisions  follow  the  trabecular;  from 
these  vessels  smaller  branches  extend  into  the  substance  of  the 
organ  and  form  capillary  plexuses  in  the  diffuse  tissue  and  around 
the  nodules.  The  blood  is  then  collected  and  returned  by  venous 
channels. 


254  PRACTICAL  HISTOLOGY 

The  lymphatics  are  also  numerous.  The  lymph  channels  form 
plexuses  that  surround  the  nodules  and  empty  into  a  peripheral 
vessel  beneath  the  fibrous  capsule. 

THE  PHARYNX 

The  pharynx  is  a  musculo-membranous  bag  that  connects  the  oral 
cavity  with  the  esophagus.  It  communicates  also  with  the  larynx, 
the  nasal  cavities  and  on  each  side  with  the  middle  ear  through 
the  auditory  tube.  There  are  three  divisions,  the  nasopharynx,  the 
oropharynx  and  the  laryngo  pharynx.  It  consists  of  three  coats 
mucous,  fibrous  and  muscular. 

The  mucous  coat  of  the  nasopharynx  is  lined  with  stratified  ciliated 
cells  that  rest  upon  a  delicate  basement  membrane  beneath  which 
there  is  the  areolar  tunica  propria.  Goblet  cells  are  also  numerous 
in  the  epithelial  layer.  In  the  tunica  propria  there  are  usually 
some  small  mucous  glands  and  lymphoid  tissue.  The  latter  is  of 
the  diffuse  form  and  solitary  nodules  are  very  numerous,  especially 
on  the  dorsal  wall.  When  these  hypertrophy  in  the  child  they  are 
called  adenoids.  This  lymphoid  tissue  represents  the  pharyngeal 
tonsil.  The  tunica  propria  is  firmly  adherent  to  the  bony  dorsal 
boundary  of  the  pharynx,  but  laterally  and  ventrally  it  is  loosely 
attached  to  the  muscles  of  the  pharynx  and  palate. 

At  the  side  of  the  nasopharynx  the  epithelial  cells  are  continuous 
with  those  of  the  auditory  tube.  The  tunica  propria  of  the  pharyn- 
geal extremity  of  the  auditory  tube  contains  a  considerable  quantity 
of  lymphoid  tissue  that  constitutes  the  tubal  tonsil. 

In  the  oropharynx  and  laryngo  pharynx  the  epithelium  is  of  the 
stratified  squamous  variety.  These  rest  upon  a  basement  membrane 
and  a  rather  thick  tunica  propria  that  contains  thin-walled  blood- 
vessels and  the  ducts  of  some  mucous  glands  that  lie  deeper.  The 
epithelial  surface  of  the  tunica  propria  is  usually  papillated. 

The  fibrous  coal  is  the  middle  portion  of  the  organ;  this  consists  of 
large  bundles  of  connective  tissue  fibers  and  numerous  yellow  elas- 
tic fibers  that  are  longitudinally  directed.  Some  of  both  kinds 
of  fibers  extend  into  the  tunica  propria  and  muscle  coat.  This 
fibrous  coat  takes  the  place  of  a  submucosa  as  it  supports  the  larger 
vessels  and  nerves. 


ALIMENTARY  TRACT  255 

The  muscle  coat  of  the  pharynx  is  the  same  throughout.  It  con- 
sists of  voluntary  striated  muscle,  the  various  constrictors  of  the 
pharynx,  that  have  an  oblique  direction.  In  places  the  muscle 
tissue  is  intimately  attached  to  the  periosteum  of  the  adjacent  bones 
but  in  other  places  it  is  not  and  here  there  is  considerable  loose 
areolar  tissue  that  serves  to  connect  the  pharynx  to  the  neighboring 
tissues  or  organs.  In  the  connective  tissue  between  the  muscle 
bundles  are  the  mucous  glands  above  mentioned. 

The  blood-vessels  and  lymphatics  are  numerous;  the  main  ves- 
sels lie  in  the  fibrous  coat  and  from  this  smaller  vessels  extend  into  the 
mucous  and  muscle  coats  and  form  plexuses  of  capillaries  in  these, 
especially  around  the  glands. 

The  nerves  are  also  numerous.  Those  from  the  cerebrospinal 
system  are  both  motor  and  sensor.  The  former  pass  to  the  voluntary 
muscles  and  the  latter  to  the  mucous  membrane.  Sympathetic 
fibers  are  also  present  and  these  pass  to  the  blood-vessels  and  glands. 

ESOPHAGUS 

The  remainder  of  the  alimentary  tract  is  tubular,  and  possesses 
four  coats,  mucous,  submucous,  muscular  and  fibrous.  The 
mucosa  is  further  subdivided  into  four  layers,  epithelium,  basement 
membrane,  tunica  propria  and  muscularis  mucosae. 

In  the  esophagus,  the  mucous  coat  is  lined  by  stratified  squamous 
cells  which  upon  the  lumen  surface  run  an  even  course.  These  rest 
upon  the  basement  membrane,  beneath  which  is  the  papillated  tunica 
propria.  These  papillae  are  tall  and  slender  and  extend  for  quite  a 
distance  into  the  epithelial  layer.  The  tunica  propria  consists  of 
yellow  elastic  and  white  fibrous  tissues,  in  which  the  capillary  vessels 
form  a  delicate  network  beneath  the  epithelium;  the  ducts  of  the 
glands  pass  through  this  layer  on  their  way  to  the  surface.  These 
ducts  are  lined  by  tall  columnar  cells  at  first  but  in  the  epithelial 
layer  these  cells  are  replaced  by  several  layers  of  flattened  elements. 
Diffuse  lymphoid  tissue  and  even  solitary  nodules  may  be  present. 
The  muscularis  muscosce  consists  of  involuntary,  nonstriated  muscle 
fibers,  circularly  and  longitudinally  arranged.  In  the  upper  portion 
of  the  esophagus,  this  layer  is  often  wanting,  but  in  the  lower  part 


256  PRACTICAL   HISTOLOGY 

it  is  always  present.     In  the  resting    condition,  the  mucous  and 
submucous  coats  are  thrown  into  longitudinal  folds. 

Although  the  general  epithelium  is  of  the  stratified  squamous 
varietv  occasionally  patches  of  ciliated,  or  columnar  epithelium  are 
found  in  the  upper  third.     These  may  be  retentions  of  fetal  cells  as 


•-r  A 


gety        - 

mSt*-        ■■-/■■■■  ,  -       •  ■    '       Zr 


-rz 


Fig.  156. — Cross-section  of  Esophagus. 
o,   Stratified  squamous  epithelium;  b,  basement  membrane;  c,  tunica  propria; 
d,  muscularis  mucosae;   e,  esophageal  gland;  /,  blood-vessel;  g,  submucosa; 
k,  outer  longitudinal  muscle;  /,  fibrous  coat;  \i,  inner  circular  muscle. 

in  fetuses  up  to  birth,  such  patches  are  frequently  found  in  the 
esophagus.  In  the  resting  condition  the  walls  of  the  esophagus  are 
in  contact  and  the  lumen  almost  obliterated.  In  this  condition  the 
mucosa  and  submucosa  are  thrown  into  extensive  longitudinal  folds. 
Some  short  branched  tubular  glands,  resembling  those  of  Ue 
cardiac  end  of  the  stomach,  are  found  in  the  upper  part  of  hie 


ALIMENTARY   TRACT  257 

esophagus.  These  tubules  are  lined  throughout  with  simple  col- 
umnar cells  as  well  as  the  neighboring  esophageal  surface.  In  ad- 
dition the  secretion  portions  may  contain  some  parietal  cells.  Al- 
though they  do  not  respond  to  stains  as  the  deep  mucous  glands  they 
are  considered  mucous  in  type.  These  glands  involve  only  the 
mucous  coat  and  are  called  the  upper  cardiac  glands  or  the  superficial 
glands  of  the  esophagus. 

The  lower  cardiac  glands  are  found  at  the  lower  part  of  the  esopha- 
gus close  to  junction  with  the  cardiac  portion  of  the  stomach. 
These  glands  are  similar  to  the  preceding  and  are  continuous  with 
the  gastric  glands. 

The  submucous  coat  is  composed  of  coarser  bundles  of  white 
fibrous  tissue,  which  forms  a  loose  network  for  the  support  of  the 
large  blood-vessel  trunks.  In  this  coat  are  seen  a  number  of  glandu- 
lar structures,  the  esophageal  glands,  which  are  apparently  mucous, 
as  they  stain  lightly  with  ordinary  stains  but  respond  well  to  the 
mucin  stains.  They  send  their  ducts  through  the  mucous  coat.  As 
the  stomach  is  approached,  these  glands  become  more  numerous, 
and  may  even  be  found  in  the  mucosa.  They  are  of  the  compound 
alveolar  type;  crescents  are  absent  in  these  glands  in  man.  In 
herbivorous  animals  these  glands  are  absent.  In  carnivorous  and 
omnivorous  animals  they  are  very  numerous  seeming  to  indicate 
that  they  are  important  in  the  chemistry  of  digestion. 

The  muscle  coat  consists  of  muscle  fibers  arranged  in  two  layers, 
inner  circular  and  outer  longitudinal.  It  is  said  that  the  layers  are 
thicker  here  than  in  any  other  part  of  the  alimentary  tract  with  the 
exception  of  the  caudal  end  of  the  intestine.  In  the  upper  third 
these  fibers  are  of  the  voluntary  striated  variety,  in  the  lower  third 
smooth  and  in  the  middle  portion,  mixed.  The  involuntary  non- 
striated  variety  continues  throughout  the  remainder  of  the  tract. 
In  the  upper  part  of  the  esophagus  the  longitudinal  muscle  is 
arranged  in  three  bands,  one  ventral  and  two  lateral.  Occasionally 
some  voluntary  fibers  are  found  in  the  lower  third  in  man,  while 
in  some  animals  these  fibers  predominate  throughout  the  esophagus. 

The  fibrous  coat  consists  of  fibro-elastic  tissues,  and  connects  the 
organ  with  surrounding  tissues.  It  sends  in  bundles  between  the 
muscle  bundles,  of  which  they  are  said  to  form  the  perimysium. 

17 


258  PRACTICAL  HISTOLOGY 

The  main  blood-vessels  lie  in  the  submucosa  and  form  a  longi- 
tudinal network.  From  this  smaller  branches  pass  to  the  mucosa, 
the  muscularis  mucosae  and  the  muscular  coat.  In  these  extensive 
capillary  plexuses  are  formed.  In  the  submucosa  special  plexus 
surround  the  glands.  The  blood  is  returned  by  venous  channels 
in  a  corresponding  course. 

The  lymphatics  are  mucous  and  submucous.  The  mucous  vessels 
start  in  the  papillae  and  connect  with  the  channels  in  the  submucosa 
which  also  receive  the  lymph  from  the  muscle  coat.  The  solitary 
nodules  present  are  usually  surrounded  by  sinus-like  lymph  vessels. 

The  nerves  are  both  myelinated  and  amyelinated.  They  form 
two  plexuses,  one  between  the  layers  of  the  muscle  coat  and  the  other 
in  the  submucous  coat.  In  these  plexuses  there  are  many  large 
ganglia  containing  large  ganglion  cells.  From  the  myenteric  plexus 
myelinated  nerve  fibers  (from  the  vagus)  pass  to  the  voluntary 
striated  muscles  where  they  terminate  in  motor  end-organs.  Other 
amyelinated  nerve  fibers  pass  to  the  smooth  muscle  tissue  of  the 
muscle  coat  and  the  muscle  of  the  vessels.  From  the  submucous 
plexus  amyelinated  fibers  pass  to  the  muscularis  mucosae  and  the 
glands  and  epithelial  lining  of  the  organ  where  they  terminate  in 
free  endings. 

STOMACH 

The  stomach  is  the  first  part  of  the  tract  in  which  the  food  rests 
for  any  length  of  time,  and  in  which  active  digestion  and  possibly 
some  absorption  occur.  Although  very  large,  it  still  represents  a 
tube,  and  has  the  four  coats  above  mentioned.  It  is  divided  into 
three  portions,  the  cardia,  fundus  and  pyloric  end.  They  pass  into 
one  another  insensibly,  and  the  structure  of  the  first  two  parts  is 
practically  the  same. 

The  mucous  coat  is  rather  thick  and  presents  a  great  change  over 
that  of  the  esophagus,  showing  a  higher  degree  of  specialization. 
The  epithelial  change  is  abrupt.  In  it  are  seen,  with  the  naked  eye, 
a  number  of  minute  depressions,  the  gastric  crypts,  or  pits,  from  which 
the  gastric  glands  extend  into  the  deeper  portions.  The  crypts  are 
0.12  to  0.25  mm.  in  diameter  and  the  longer  and  deeper  ones  are 
near  the  pyloric  portion.     Between  or  bounding  the  pits,  are  the 


ALIMENTARY   TRACT  259 

inter  glandular  projections  (plica  villosce).  Each  gland  consists  of 
mouth,  neck  and  fundus,  or  secretory  portion,  and  is  lined  by  simple 
epithelial  cells. 

The  cells  rest  upon  a  basement  membrane,  which,  in  turn,  rests  upon 
the  tunica  propria.  The  latter  forms  the  core  of  the  interglandular 
projections  that  form  the  boundaries  of  the  pits.  Between  the 
glands,  the  tunica  propria  consists  of  narrow  bands  of  the  areolar 
tissue,  which  contains  a  great  deal  of  diffuse  lymphoid  tissue,  bundles 
of  smooth  muscle  fibers  from  the  muscularis  mucosae,  and  capillaries, 
both  vascular  and  lymphatic,  in  great  numbers.  In  places,  the 
lymphoid  tissue  is  collected  into  solitary  nodules  that  are  lens-shaped, 
and  are  called  the  lenticular  nodules.  These  are  numerous  in  the 
pyloric  end.  The  mucosa  is  bounded  externally  by  the  muscularis 
mucosa,  which  consists  of  two  layers  of  smooth  muscle  fibers, 
arranged  as  inner  circular  and  outer  Imigiludinal  layers. 

In  the  cardiac  and  fundal  portions,  the  secretory  portions  of  the 
glands  are  chiefly  of  the  simple  tubular  variety.  The  mouth  is  short, 
with  the  neck  and  fundus  of  about  the  same  length.  In  the  neck 
and  fundus,  are  found  two  varieties  of  low  columnar  cells,  the  chief, 
peptic,  or  adelomorphous  cells,  and  the  large  delomorphous,  acid,  or 
oxyntic  cells. 

The  surface,  or  true  lining  cells  of  the  stomach  are  tall  and  narrow 
elements  that  line  the  mouths  of  the  glands,  the  gastric  pits  and  cover 
the  interglandular  projection,  or  parts  intervening  between  the  pits. 
In  the  resting  stage  the  basal  part  contains  the  nucleus  and  the 
cytoplasm  is  granular;  the  distal  cytoplasm  is  clear  and  stains 
lightly.  They  are  mainly  goblet  cells  and  secrete  a  mucous  sub- 
stance that  is  probably  of  a  protective  nature.  Cuticular  borders 
are  not  prominent  and  terminal  bars  are  to  be  found  at  their  distal 
extremities.  These  cells  form  a  broad  band  of  palely  stained  pro- 
toplasm in  which  the  basally  placed,  darkly  staining  nuclei  form  a 
row  of  closely  placed  bodies.  The  lateral  boundaries  of  the  cells 
are  not  distinct,  but  the  nucleus  of  each  indicates  the  breadth  of 
the  cell.  Altogether  they  give  a  feather-like_  appearance  to  the 
interglandular  projections. 

The  peptic  cells  are  low  columnar,  or  pyramidarelements  and  are 
more  numerous  in  the  fundi  than  the  necks  of  the  glands.     The 


260 


PRACTICAL   HISTOLOGY 


nucleus  is  usually  circular  or  oval  and  contains  considerable  chro- 
matin. The  granular  cytoplasm  has  an  affinity  for  hematoxylin 
and  appears  bluish  when  characteristically  stained.  During  the 
resting  stage  the  cells  become  so  swollen  as  to  occlude  the  lumen  of 


Fig.  157. — Cross-section  of  Segment  of  Stomach. 
A,  Cardiac  Region — a,  mucous  coat;  b,  submucous  coat;  c,  muscular  coat; 
d,  fibrous  coat;  e,  epithelium;  /,  interglandular  projection;  g,  basement 
membrane;  h,  gastric  pit;  i,  neck  of  gland;  k,  acid  cell;  I,  tunica  propria; 
m,  n,  layers  of  muscularis  mucosae;  o,  submucosa;  p,  circular  layer  of  mus- 
cular coat;  q,  longitudinal  layer  of  muscular  coat;  r,  oblique  layer  of  muscular 
coat;  s,  white  fibrous  tissue  layer  containing  the  nerve  plexus  of  Auerbach. 
B,  Gland  of  Cardiac  Region  of  Stomach — a,  gastric  pit;  b,  columnar  epi- 
thelium; c,  goblet  cell;  d,  basement  membrane;  e,  tunica  propria  of  inter- 
glandular projection;  /,  neck  of  gland;  g,  acid  cell;  h,  peptic  cell. 


the  gland.  The  granules  increase  in  number  in  the  distal  portion 
of  the  cell,  forming  a  broad  zone.  These  are  zymogen  granules  and 
are  derived  from  the  prozymogen  granules  that  occupy  the  basal 
portion  of  the  cell.     These  prozymogen  granules  are  in  the  form  of 


ALIMENTARY   TRACT  26 1 

small  rods  and  are  so  placed  as  to  give  a  striated  appearance  to  the 
basal  part  of  the  cell.  These  are  said  to  respond  readily  to  toluidin 
blue  or  iron  hematoxylin.  After  secretion  these  cells  are  greatly 
reduced  in  size  and  are  less  granular. 

The  acid  or  oxyntic  cells  are  readily  distinguished  from  the  others 
by  their  size,  shape,  and  affinity  for  acid  stains.  They  are  very 
large,  oval,  or  triangular  elements,  most  numerous  in  the  necks, 
but  also  scattered  in  the  fundus.  They  are  found  along  the  wall 
of  the  tubule,  and  usually  beneath  the  peptic  cell,  hence  the  term 
parietal,  or  wall,  cell.  The  nucleus  is  quite  large  (there  may  be  two) 
and  centrally  located. 

These  cells  are  most  numerous  in  the  neck  of  the  glands  where 
they  are  more  oval  in  shape.  In  the  fundus  of  the  gland  they  are 
somewhat  triangular  in  form  while  in  the  intermediate  part  of  the 
gland  tubule  they  are  said  to  be  sort  of  wedge-shaped,  or  pyramidal  in 
outline.  The  homogeneous,  or  finely  granular  cytoplasm  contains 
an  elaborate,  basket-like  system  of  secretory  canals  that  carry  the 
secretion  of  these  cells  to  the  lumen  of  the  tubule.  This  canalicular 
system  can  be  outlined  by  the  silver,  nitrate  method. 

The  appearance  of  the  parietal  cells  alters  with  its  stages  of  rest 
and  activity.  During  fasting  the  cells  are  much  smaller  and  more 
angular  in  outline,  and  may  leave  their  position  against  the  wall 
of  the  tubule.  During  digestion  these  cells  increase  greatly 
in  size. 

Although  these  are  called  the  acid  cells  and  are  supposed  to  secrete 
the  hydrochloric  acid  of  the  gastric  juice  this  seems  improbable  as 
the  reaction  of  the  cytoplasm  is  neutral  or  alkaline  and  contains 
chiefly  chlorids.  It  is  thought  that  an  organic  chlorid  is  formed 
by  the  cells  and  when  this  is  passed  to  the  lumen  of  the  gland  the 
hydrochloric  acid  is  liberated.  The  recent  work  of  Hammett  leads 
him  to  believe  that  hydrochloric  acid  is  present  in  the  parietal  cells. 

In  some  animals  the  parietal  cells  are  placed  in  special  depressions 
of  the  basement  membrane  and  communicate  with  the  gland  proper 
by  only  a  narrow  opening.  In  some  amphibia  the  glands  of  the 
fundus  of  the  stomach  contain  only  the  acid  cells;  their  pepsin- 
forming  cells  are  apparently  located  in  glands  in  the  esophagus. 
In  birds  the  main  tubules  of  the  glandular  stomach  are  lined  only 


262  PRACTICAL   HISTOLOGY 

with  peptic  cells  and  the  acid  cells  line  the  secondary,  or  offshoot 
tubules  alone. 

The  affinity  for  acid  stains  is  pronounced.  With  eosin,  they  are 
distinctly  red,  while  with  acid  fuchsin  they  are  colored  a  very  much 
deeper  red. 

In  the  first  portion  of  the  fundus,  the  glands  are  chiefly  of  the 
simple  tubular  variety.  As  the  pyloric  end  is  approached,  the 
branched  tubulars  begin  to  increase,  so  that  they  form  the  predom- 
inating variety  in  this  end.  There  is  also  a  marked  change  in  the 
lining  cells.  The  acid  cells  become  rapidly  fewer  in  number,  and, 
in  the  pyloric  end,  are  but~seldom  seen.  One  can,  therefore,  be 
safe  in  saying  that  a  section  containing  a  number  of  acid  cells  is 
from  the  fundus,  or  cardia. 

Around  the  cardiac  orifice  is  a  zone  5  to  40  mm.  wide  where  the 
special  tubulo-alveolar  cardiac  glands  are  found.  The  cells  of  these 
glands  are  chiefly  of  the  mucous  type;  other  cells  similar  to  the 
chief  and  acid  cells  of  the  fundus  glands  and  the  peptic  cells  of  the 
pyloric  glands  are  found.  These  glands  represent  retrogressive 
fundus  glands  (Bensley).  According  to  Ellenberger  and  others 
the  true  cardiac  glands  contain  acid  cells  and  secrete  an  amylolytic 
ferment. 

In  the  pyloric  canal  the  mucosa  is  thicker  and  the  glands  are  of 
the  branched  tubular  variety.  The  gastric  crypts  are  deeper,  the 
mouths  of  the  glands  are  longer  and  the  fundi  and  necks  are  compara- 
tively shorter.  Into  each  mouth  or  crypt  a  number  of  secreting 
tubules  pour  their  secretion  and  these  tubules  are  all  the  branches  of 
one  duct.  The  fundal  or  secreting  portions  may  be  coiled.  These 
pyloric  glands  are  said  to  occupy  the  pyloric  fifth  of  the  stomach, 
according  to  Piersol. 

The  inter  glandular  projections  are  covered  and  the  pits  and  gland 
ducts  are  lined  with  the  same  kind  of  tall,  slender  columnar  and 
goblet  cells  seen  in  the  cardiac  portion.  This  variety  of  cell  is  more 
extensive,  however,  on  account  of  the  greater  amount  of  surface 
covered.  The  secreting  portions  of  the  glands  present  an  entirely 
different  appearance  than  the  corresponding  portions  of  the  fundal 
glands.  In  the  first  place,  they  are  not  straight  as  in  the  cardia 
and  fundus;  in  the  second  place,  the  branches  of  one  duct  are  usually 


ALIMENTARY   TRACT 


26 


grouped  closely  together  and  seem  to  be  distinctly  separated  from 
their  neighbors  by  denser  tunica  propria  resembling  septa,  or  tiny 
capsules;  thirdly,  the  cells  are  different  in  form  and  different  in  stain 
reaction  than  those  of  the  cardia  and  fundus;  lastly,  the  cells  are 
usually  of  only  one  variety  and  the  lumen  of  the  secretory  tubules 
is  broader  than  in  the  other  glands  of  the  stomach. 

The  cells  are  said  to  be  of  the  peptic  variety  but  they  differ  from 
those  of  the  cardia  and  fundus.     Each  cell  is  taller  and  broader  than 


Fig.  158. — Longitudinal  Section  of  Segment  of  Pyloric  Region  of  Stomach. 

a,  Mucous  coat;  b,  submucous  coat;  c,  muscular  coat;  d,  fibrous  coat;  e,  inter- 
glandular  projection;  /,  epithelium;  g,  basement  membrane;  h,  gastric 
pit;  i,  pyloric  glands;  k,  tunica  propria;  I,  muscularis  mucosae;  m,  blood- 
vessel; n,  connective  tissue  in  muscular  coat;  o,  inner  circular  layer  of  muscle; 
■p,  outer  longitudinal  layer  of  muscle. 


the  ordinary  peptic  cell  and  represents  a  distinct  columnar  element. 
They  are  sharply  delimited  and  differentiated  from  the  cells  of  the 
ducts  and  interglandular  projections.  The  cytoplasm  is  clear  and 
responds  only  faintly  to  the  ordinary  stains.  In  the  resting  stage 
the  cytoplasm  is  finely  granular.  The  oval  nucleus  stains  readily 
and  occupies  a  basal  location.  As  the  pyloro-duodenal  junction 
is  reached,  the  glands  become  shorter  and  less  numerous,  and  some 
may  even  extend  into  the  submucosa.  Intestinal  crypts  have  been 
found  in  the  stomach.     The  interglandular  projections  become  longer, 


264  PRACTICAL  HISTOLOGY 

and  resemble,  somewhat,  the  villi  of  the  small  intestine  but  they  are 
not  true  villi.  The  pyloric  glands  may  extend  from  6  to  14  cm. 
from  the  pyloro-duodenal  junction. 

The  mucosa  and  submucosa  are  thrown  into  large,  longitudinal 
folds,  the  rugce,  in  the  empty  contracted  stomach.  These  folds 
and  glands  increase  greatly  the  absorptive  and  secretory  surfaces. 
As  the  stomach  fills  these  folds  become  reduced  in  size  and  when  the 
stomach  is  fully  distended  they  are  gone.  This  provision  permits 
of  great  distension  of  the  organ  without  injury  to  the  mucosa. 

In  addition  to  these  glands  crypts  of  LieberkUhnh&ve  been  described 
in  the  stomach.  These  crypts  are  more  numerous  in  the  transition 
zone  (between  fundus  to  pyloric  canal),  although  some  have  been 
found  scattered  in  other  parts.  These  resemble  the  glands  of  the 
mucosa  of  the  small  intestine;  they  are  simple  tubular  in  form  and 
are  lined  with  simple  columnar  cells  with  striated  borders  and 
occasionally  goblet  cells  are  seen.  In  the  fundi  of  these  glands 
cells  of  Paneth  are  said  to  be  present. 

The  submucous  coat  consists  of  areolar  tissue.  The  fibers  and 
bundles  are  usually  coarser  than  those  found  in  the  tunica  propria 
and  the  meshes  formed  by  these  bundles  are  also  larger.  This  is 
because  the  larger  blood-vessels  and  lymphatics  are  here  and  the 
submucosa  might  readily  be  called  the  vascular  coat.  This  coat 
stains  lightly  because  diffuse  lymphoid  tissue  is  absent.  In  this 
coat  is  located  the  submucous  plexus  of  nerves  that  supplies  the 
muscularis  mucosae  and  the  epithelium  of  the  organ.  The  sub- 
mucosa forms  a  loose  distensible  coat  connecting  the  muscular  and 
mucous  coats  and  forms  the  central  portion  of  the  rugous  folds. 

The  muscular  coat  consists  of  smooth  muscle  tissue  arranged  in 
three  layers.  Of  these  the  inner  is  oblique.  These  fibers  are  con- 
tinuous with  the  circular  fibers  of  the  left  side  of  the  esophagus 
but  they  do  not  form  a  complete  layer.  The  middle,  circular  fibers 
form  a  complete  layer  and  are  continuous  with  the  circular  fibers 
of  the  esophagus.  The  circular  fibers  form  ring-like  masses  that 
start  at  the  fundus  becoming  at  first  larger  and  then  smaller  as  the 
pylorus  is  approached.  At  the  pyloric  orifice  they  form  a  very 
thick  ring  called  the  sphincter  pylori  muscle.  The  outer,  longitudinal 
layer  is  continuous  with  the  corresponding  layer  of  the  esophagus. 


ALIMENTARY   TRACT  265 

These  fibers  radiate  from  the  cardiac  orifice  and  are  most  numerous 
along  the  curvatures.  Although  they  form  only  a  thin  layer  on 
the  surface  they  become  increased  in  number  toward  the  pylorus 
and  become  continuous  with  the  longitudnal  layer  of  the  intestine. 
Between  the  circular  and  longitudinal  layers  is  the  myenteric 
plexus  of  nerves  for  this  coat. 

The  external,  or  flbroserous  coat,  consists  of  a  layer  of  the  perito- 
neum, a  serous  membrane.  This  consists,  externally,  of  a  single 
layer  of  endothelial  cells  resting  upon  the  fibroelastic  subendothelial 
tissue.  It  invests  all  but  a  very  small  part  of  the  stomach.  At  the 
curvatures  it  continues  away  from  the  organ  forming  the  omenta 
and  it  is  at  these  regions  that  the  vessels  gain  access  to  the  stomach. 
Beneath  this  is  a  thin  layer  of  areolar  tissue  that  constitutes  the 
fibrous  coat.  Some  of  its  fibers  pass  in  between  the  bundles  of 
muscle  fibers  of  the  longitudinal  layer  and  blend  with  the  perimysial 
sheaths. 

The  blood-vessels,  lymphatics  and  nerves  will  be  considered  with 
those  of  the  intestinal  tract. 

SMALL  INTESTINE 

The  intestinal  tract  consists  of  two  main  portions,  the  small  and 
large  intestines.  These  each  have  their  subdivisions,  which  usually 
differ  from  one  another. 

The  small  intestine  is  divided  into  duodenum,  jejunum  and 
ileum.  They  all  have  the  same  general  structure.  This  will  first 
be  described,  and  then  the  differences  studied. 

There  are  four  coats,  mucosa,  submucosa,  muscularis  and  fibrosa, 
or  serosa. 

The  mucosa  has  four  layers,  epithelium,  basement  membrane, 
tunica  propria  and  muscularis  mucosce.  As  is  the  case  with  the 
mucosa  of  the  stomach,  the  epithelium  is  evaginated  in  the  form  of 
an  immense  number  of  tiny  glands  that  are  all  of  the  simple  tubular 
variety.  The  tunica  propria  and  epithelium  between  the  glands  are 
invaginated  into  the  lumen  of  the  intestine  in  the  form  of  simple, 
finger-like  projections,  the  villi,  that  resemble  the  interglandular 
projections  of  the  stomach  but  are  a  little  different  in  structure  and 


266 


PRACTICAL  HISTOLOGY 


entirely  different  in  function.  Through  the  formation  of  the  glands 
and  plicae  circulares,  to  be  described  later,  the  secretory  surface  of 
the  tubular  intestine  is  enormously  increased.  Through  the  for- 
mation of  the  villi  and  the  plicae  circulares  the  absorptive  surface  is 
also  enormously  increased. 


Epithelium. 


Tunica  propria. 


Portion   of   a  capillary 
blood  vessel. 


Cuticular  border. 


Nucleus    of  a  lympho- 
cyte. 


Tangential  section  of  a 
goblet  cell. 


-    Mucus  in  a  goblet  cell. 


Nucleus  of  a  smooth  muscle  fiber.  Central  lymphatic  vessel. 

Fig.  159. — Longitudinal  Section  through  the  Apex  of  the  Villus 

of  a  Dog.     X  360. 
The  goblet  cells  contain  less  mucus  as  they  approach  the  summit  of  the  villus. 

The  epithelial  cells  are  columnar  in  type  but  vary  in  structure,  those 
covering  the  villi  differing  from  those  that  line  the  glands.  These 
cells  rest  upon  a  thin  basement  membrane,  of  a  reticular  nature, 
which  is  supported  by  the  tunica  propria.  The  basement  membrane 
like  the  epithelial  cells  has  a  very  sinuous  course  passing  in  a  con- 
tinuous manner  over  the  villi  and  down  into  the  glands. 


ALIMENTARY   TRACT  267 

The  tunica  propria  consists  of  areolar  tissue.  This  fills  in  the 
space  between  the  glands  and  the  muscularis  mucosae  and  forms  the 
core  of  the  villi.  It  contains  a  great  deal  of  diffuse  lymphoid  tissue 
and  the  amount  varies  at  different  times  as  the  leukocytes  come  and 
go.  Occasionally  Peyer's  patches  project  through  the  muscularis 
mucosa?  into  the  mucosa.  The  abundance  of  the  leukocytes  gives 
tunica  propria  a  dark  appearance  and  hides  the  areolar  tissue.  In 
addition  vascular  and  lymphatic  capillaries  are  very  numerous. 
The  nerves  from  the  submucous  plexus  pass  through  the  tunica 
propria  to  their  terminations. 

The  muscularis  mucosa  consists  of  smooth  muscle  tissue  arranged 
into  two  layers.  The  inner  layer  consists  of  circularly  arranged 
fibers  and  the  outer  of  longitudinally  directed  fibers.  It  runs  an 
unbroken  course  usually  but  in  the  ileum  it  may  be  broken  in  places 
by  the  nodules  of  a  Peyer's  patch  that  is  invading  the  mucosa.  The 
muscle  fibers  found  in  the  villi  are  said  to  be  derived  from  the  muscu- 
laris mucosae. 

The  intestinal  crypts,  or  glands  of  Lieberkiihn  are  of  the  simple 
tubular  variety  and  involve  only  the  epithelium,  basement  mem- 
brane and  tunica  propria.  These  are  evaginations  of  the  epithelium 
and  basement  membrane  that  measure  0.2  to  0.3  mm.  in  depth  and 
extend  in  a  straight  course  almost  to  the  muscularis  mucosae.  The 
tunica  propria  that  surrounds  them  and  separates  one  from  the  other 
is  filled  with  diffuse  lymphoid  tissue. 

Lining  the  mouths  of  the  glands  and  then  continuing  over  the 
villi  are  goblet  cells  in  various  stages  of  secretion.  When  these  cells 
have  discharged  their  secretion  they  are  tall  columnar  elements  with 
cytoplasm  that  stains  fairly  darkly;  when  they  are  full  of  secretion 
they  are  goblet-shaped  and  stain  very  lightly.  A  cuticular  border  is 
distinct.  In  the  necks  and  parts  of  the  fundi  of  the  glands  the  cells 
are  of  the  simple  columnar  type.  The  cytoplasm  of  these  cells  is 
slightly  granular  and  contains  no  mucin  or  fat.  A  cuticular  border 
is  not  well  developed.  They  are  supposed  to  be  indifferent  cells 
which  by  mitosis  produce  daughter  cells  that  may  become  differen- 
tiated into  the  goblet  cells  of  the  neck  and  villus  or  the  glandular  cells  in 
the  fundus  of  the  glands.  The  remaining  portion  of  the  fundus  of 
each  gland  is  lined  by  these  simple  columnar  cells  but  in  the  bottom 


268  PRACTICAL  HISTOLOGY 

of  the  fundus  are  the  cells  of  Paneth.  These  are  low  columnar,  or 
pyramidal  elements  in  which  the  cytoplasm  is  coarsely  granular; 
in  some  of  the  cells  these  granules  respond  to  the  plasmatic  stains 
and  in  others  to  the  nuclear  stains.  These  are  no  doubt  secretion 
granules  in  the  various  stages  of  elaboration.  Other  granule  cells 
have  recently  been  described.  One  of  these,  the  acidophilic  cell, 
has  fine  granules  that  respond  to  the  acid  stains;  the  other,  the 
chromaffin  cells  (called  yellow  cells  by  Schmidt)  contain  fine  granules 
of  chromaffin.  These  cells  are  found  both  in  the  glands  and  upon 
the  villi  and  are  apparently  independent  of  all  of  the  other  cells. 
Cells  resembling  the  chromaffin  cells  have  been  found  in  the  glands 
of  Brunner  of  the  duodenum.  Between  the  various  cells  of  glands 
and  villi  leukocytes  are  frequently  seen. 

The  villi  are  little  finger-like  projections  of  the  tunica  propria 
covered  by  the  basement  membrane  and  simple  columnar  cells. 
They  are  enormous  in  number  and  extend  throughout  the  length 
of  the  small  intestine  and  constitute  one  of  its  most  important 
characteristics.  They  increase  greatly  the  absorptive  surface  of 
this  organ  and  vary  somewhat  in  number,  shape  and  height  in  the 
different  divisions  of  the  intestine.  The  base  of  the  villus  is  at  the 
level  of  the  mouths  of  the  glands  and  its  tunica  propria  core  is 
directly  continuous  with  the  tunica  propria  that  lies  between  the 
glands.     The  tip  of  the  villus  extends  into  the  lumen  of  the  intestine. 

Each  villus  is  from  0.2  to  i  mm.  in  height.  The  center  consists  of 
tunica  propria  that  consists  of  delicate  areolar  tissue  containing  a 
great  deal  of  diffuse  lymphoid  tissue.  Although  the  amount  of 
this  is  constantly  variable  there  is  usually  enough  present  to  hide 
the  areolar  tissue  and  the  other  structures.  In  addition  there  are 
numerous  blood  capillaries,  smooth  muscle  fibers  and  a  dilated  lymph 
capillary  in  the  center  called  a  lacteal.  The  smooth  muscle  fibers  are 
longitudinally  arranged  around  the  lacteal  and  serve  to  retract  the 
villus.  Those  fibers  near  the  tip  of  the  villus  are  attached  to  the 
basement  membrane,  the  muscle  fibers  branching  to  make  this 
attachment.  The  lacteal  is  the  starting  point  of  the  lymphatic 
vessels  of  the  small  intestine.  They  are  simply  large  lymph  capil- 
laries and  extend  through  the  villus  toward  the  muscularis  mucosae 
where  they  empty  into  a  plexus  of  lymph  vessels.     By  contraction 


ALIMENTARY   TRACT 


269 


of  the  muscle  of  the  villus  this  structure  is  shortened  and  the  lacteal 
pressed  upon  and  emptied.  The  valve  at  the  end  of  the  lacteal, 
where  it  connects  with  the  plexus,  prevents  regurgitation  of  the 
lymph.     Occasionally  two  lacteals  may  be  found  in  one  villus. 

The  basement  membrane  is  a  thin  reticulated  structure  that  sup- 
ports the  epithelial  cells.     These  cells  consist  of  a  single  layer  of 


Mucous  __ 
coat 


Submucous, 
coat 


Muscle- 
coat 


FibroserousB 
coat 


«*  w 


v ','■  J     • 


'«**>*1 


Fig.  160. — Longitudinal  Section  of  the  Human  Duodenum. 
a,  Villus;  b,  gland  of  Brunner.      (Photograph.     Obj.  32  mm.,  oc.  7.5  X.) 


columnar  elements  that  are  really  goblet  cells  in  different  stages  of 
secretion.  The  discharged  cells  are  narrow  columnar  cells,  the 
cytoplasm  is  slightly  granular  and  stains  more  darkly  than  in  later 
stages.  The  nucleus  is  near  the  basal  extremity  of  the  cell  and  is 
usually  thicker  than  the  band  of  cytoplasm.  In  the  resting  stage  the 
secretion    makes   its   appearance   in    the   form   of    fine    granules, 


270  PRACTICAL  HISTOLOGY 

mucinogen,  which  increase  in  number  and  size  and  respond  to  special 
stains.  These  form  a  goblet-like  mass  that  crowds  the  remains  of 
the  cytoplasm  and  the  nucleus  to  the  basal  part  of  the  cell.  When 
secretion  occurs  these  granules  absorb  water,  swell  and  run  together 
to  form  a  single  droplet  of  mucin  that  is  discharged  into  the  lumen 
of  the  intestine.  Each  goblet  cell  possesses  a  diplosome  that  lies 
near  the  middle  of  the  peripheral  half  of  the  cell.  It  is  in  this 
region  that  the  mucus  is  formed. 

The  villi  of  the  duodenal  portion  of  the  small  intestine  are  from 
0.2  to  0.5  mm.  in  height,  flat  and  leaf -like  in  form  and  most  numerous. 
In  the  jejunum  they  are  0.5  to  0.7  mm.  in  height,  club-shaped.  In 
the  ileum  they  are  short  and  filiform  and  fewer  in  number.  Accord- 
ing to  Piersol  the  number  per  square  millimeter  is  as  follows:  Duo- 
denum and  jejunum,  24  to  40;  ileum  15  to  30.  The  shape  and  height 
are  said,  by  Johnson,  to  vary  according  to  the  state  of  distension 
of  the  intestine. 

The  mucosa  and  submucosa  are  thrown  into  folds  that  have  a 
circular  direction  and  are  called  the  plica  circulares,  or  valvules 
conniventes.  These  extend  usually  about  two-thirds  of  the  way 
around  the  bowel  though  some  form  complete  circles  and  others 
form  spirals  of  one  or  more  turns.  The  spirals  may  occur  individu- 
ally or  in  groups  of  two  or  three.  At  their  highest  points  these  folds 
are  about  8  mm.  in  height.  They  increase  the  absorptive  surface 
and  are  permanent,  that  is  no  matter  how  much  the  bowel  is  dis- 
tended within  the  normal  limits  these  folds  are  always  present. 
These  folds  do  not  begin  to  appear  until  a  short  distance  from  the 
pyloric  orifice  so  that  the  first  part  of  the  duodenum  is  practically 
smooth.  The  are  quite  large  just  beyond  where  the  conjoined  bile 
and  pancreatic  ducts  open  and  are  nearer  one  another  here.  Here 
they  are  about  the  height  of  a  fold  apart.  In  the  middle  of  the 
jejunum  and  on  they  become  smaller  and  more  widely  separated  and 
ultimately  disappear  in  the  lower  end  of  the  ileum. 

The  duodenum  shows  the  general  characteristics  of  the  small 
intestine  and  in  addition  possesses  the  glands  of  Brunner,  or  duodenal 
glands  that  are  characteristic  of  this  division  of  the  small  bowel. 
These  are  branched  tubular  structures  that  are  located  in  the  sub- 
mucosa.    Each  is  small  and  according  to  some  tubuloalveolar;  they 


ALIMENTARY   TRACT  27 1 

are  most  numerous  in  the  first  part  of  the  duodenum  and  may 
sometimes  break  through  the  muscularis  mucosae  and  lie  partly  in 
the  mucosa.  The  secreting  cells  stain  very  lightly  giving  the  idea 
of  a  mucous  gland.  A  mucin  reaction  can  be  obtained.  In  the 
resting  condition,  just  after  discharge,  the  cells  appear  small, 
shrunken  and  granular.  During  the  accumulation  of  the  secretion 
the  cells  become  larger,  swollen  and  clear.     As  the  ducts  leave  the 

7  56 


■ 


r$m  f 


K. 


Fig.  161. — Cross-section  of  Duodenum. 
1,   Mucous  coat;  2,  submucous  coat;  3,  muscular  coat;  4,  fibrous  coat;  5,  6, 
villi;  7,  epithelium  of  villus;  8,  muscularis  mucosae;  9,  glands  of  Brunner. 

gland  they  run  a  somewhat  irregular  course  through  the  submucosa 
and  muscularis  mucosae  and  mucous  coats  and  empty  their  secre- 
tion at  the  bases  of  the  villi.  \ 

The  ileal  portion  of  the  small  intestine  is  characterized  by  the 
presence  of  the  agminated  nodules,  or  Peyer's  patches.  These  are  a 
form  of  lymphoid  tissue.  Each  patch  is  usually  located  in  the 
submucosa  but  at  times  one  may  break  through  the  muscularis 
mucosae  and  some  of  the  nodules  lie  in  the  mucosa.  In  the  areas  over 
such  nodules  the  glands  are  usually  absent  but  those  at  the  edges  of 
the  nodule  may  form  a  circle  about  it;  the  villi  may  also  be  absent 
here.  Each  patch  consists  of  from  ten  to  sixty  solitary  nodules  in 
one  distinct  group.     Each  solitary  nodule  shows  a  germinal  cen- 


272 


PRACTICAL   HISTOLOGY 


ter  and  may  be  surrounded  by  a  partial  or  complete  delicate  capsule 
of  white  fibrous  tissue.  Each  patch  may  be  4  cm.  in  length,  12 
to  25  mm.  in  width  and  is  usually  placed  opposite  to  the  attachment 


■  ■ 


-I 

~m 


-   V»>p3^- 


■ 


■  ■ 


■h 

■  8 
'/ 

"  e 

d 


U  i  i 


iaS* 


.    :  ■ "  , 


V 


Fig.  162. — Cross-section  of  Ileum. 
a,  Villus;  b,  epithelium;  c,  tunica  propria  of  villi;  d,  intestinal  gland;  e,  tunica 
propria;  /,  /,  muscularis  mucosae;  g,  blood-vessel;  h,  submucosa;  i,  circular 
muscle  layer;  k,  longitudinal  muscle  layer;  I,  peritoneal  layer;  m,  fibrous 
coat;  n,  nodules  of  the  Peyer's  patch. 

of  the  mesentery.  They  are  most  numerous  in  the  lower  part  of  the 
ileum  and  are  closer  together  here.  Some  state  that  they  are 
found  also  in  the  jejunum  and  in  the  caput  coli.  There  are  said  to 
be  twenty  to  thirty  of  these  on  the  average  though  as  many  as 


ALIMENTARY   TRACT  273 

forty-five  have  been  found  in  young  individuals.  They  are  most 
marked  in  the  young  gradually  decrease,  in  number  toward  middle 
age  and  in  the  aged  may  be  almost  entirely  absent.  They  are  the 
seats  of  the  ulcers  in  typhoid  fever. 

Absorption  takes  place  after  the  ingested  food  has  been  acted  upon 
by  the  various  juices  of  the  stomach,  small  intestine,  pancreas  and 
liver.  This  process  of  absorption  is  carried  on  chiefly  by  the  villi 
of  the  small  intestine.  By  the  "selective  action"  of  the  simple 
columnar  cells  covering  the  villi  the  water  and  inorganic  salts  are 
passed  through  and  ultimately  reach  the  blood-vessels.  All  of 
the  sugars,  except  possibly  lactose,  are  converted  into  levulose  and 


S!?15h&J^1SSS 


Fig.  163. — An  Agminated  Nodule  of  the  Ileum  of  a  Cat. 
(Photograph.     Obj.  48  mm.) 

dextrose  and  as  such  are  taken  into  the  epithelial  cells  and  trans- 
ferred to  the  blood-vessels.  In  whatever  form  the  carbohydrates 
are  absorbed  they  never  leave  these  cells  except  in  the  form  of 
levulose  or  dextrose.  Proteins  are  converted  into  peptones  by  the 
digestive  fluids  and  as  such  are  absorbed  by  the  epithelial  cells  of 
the  villi.  Native  proteins  are  also  absorbed  by  the  mucosa  of 
the  large  intestine.  After  absorption  the  epithelial  cells  convert 
these  peptones  into  plasma-albumin  and  as  such  are  given  over  to 
the  blood-vessels.  Recent  investigation  seems  to  point  to  the 
fact  that  the  end  products  of  protein  digestion  are  not  peptones 
but  less  complex  bodies,  as  polypeptids,  peptids  and  amido-acids. 
It  is  these  simple  products  that  the  epithelial  cells  convert  into  plas- 
ma-albumin and  plasma-globulin. 
Fats  are  believed,  by  some  investigators,  to  be  converted  into  an 

18 


274  PRACTICAL  HISTOLOGY 

emulsion  during  digestion  and  from  this  emulsion  the  fat  globules 
are  taken  by  the  epithelial  cells  and  passed  through  them  to  the 
lymph  vessels.  Others  believe  that  as  a  result  of  digestion,  fats 
are  converted  into  soaps  and  glycerin.  The  epithelial  cells  take 
these  and  reconstruct  fat  within  the  cell  bodies  and  the  fat  is  then 
passed  to  the  lymph  vessels  where  with  the  lymph  they  constitute 
the  chyle. 

If  parts  of  the  small  intestine  of  animals  fed  upon  rich  fatty 
foods  be  fixed  in  osmic  acid  solutions  and  sectioned,  the  fat  in  the 
tissues  will  be  seen  stained  black.  In  the  epithelial  cells  of  the 
villi  the  fat  droplets  are  most  numerous  and  larger  in  the  ends  of 
the  cells  toward  the  lumen  of  the  bowel.  This  would  seem  to  in- 
dicate the  second  theory  and  that  the  cells  had  taken  these  saponi- 
fication products  and  reconstructed  fat.  These  droplets  are  then 
said  to  be  passed  by  the  epithelial  cells  into  the  intercellular  spaces 
of  the  tunica  propria.  Here  the  fat  is  seen  between  and  in  the 
lymphocytes  and  also  in  the  lacteals.  It  is  supposed  that  the 
lymphocytes  assist  in  the  transference  and  passage  of  the  fat  to  the 
lacteals;  possibly  the  endothelial  cells  of  the  lacteals  assist  also  in 
this  process.  Disintegrating  leukocytes  with  fat  in  their  cytoplasm 
are  found  in  the  lacteals. 

The  muscularis  mucosae  consists  of  two  layers  of  smooth  muscle 
fibers  arranged  (inner)  circularly  and  (outer)  longitudinally.  From 
it  bundles  are  sent  up  into  the  villi. 

LARGE  INTESTINE 

This  consists  of  cecum,  colon,  rectum  and  appendix.  The  struc- 
ture of  all  is  practically  the  same. 

The  mucosa  contains  simple  tubular  glands,  crypts  of  Lieberkiihn, 
which  are  usually  longer,  broader  and  more  numerous  than  those  of 
the  small  intestine,  measuring  0.4  to  0.6  mm.  in  depth.  The  cells 
lining  these  are  goblet  cells.  The  tunica  propria  contains  a  great  deal 
of  diffuse  lymphoid  tissue  that  is  often  collected  into  solitary  nodules 
that  show  germinal  centers.  Plicce  circulares,  villi  and  cells  of  Paneth 
are  absent.  Smooth  muscle  fibers  may  extend  from  the  muscularis 
mucosae  to  the  basement  membrane. 


ALIMENTARY   TRACT 


275 


The  outer  three  coats  are  like  those  of  the  small  intestine,  except 
for  difference  in  the  muscular  coat.  The  longitudinal  fibers  are 
usually  thin  except  where  they  form  the  three  bands,  the  tcenice  coli, 
which  are  about  one-sixth  shorter  than  the  bowel.  These  act  as  a 
purse  string  to  the  intestine,  and  cause  it  to  be  thrown  into  a  number 
sacculations.  If  the  bands  be  removed,  the  sacculations  disappear. 
They  extend  from  the  cecum  to  the  beginning  of  the  rectum. 


5^gp£S£*sl_^:_  ■-.,-" 


:~:<S. 


WgZ 


•    ■■        •       '  ' 

Fig.    164. — Cross-section  of  Segment  of  Colon. 

a,  Mucous  coat;  b,  submucous  coat;  c,  muscular  coat;  d,  fibrous  coat;  e,  columnar 
cell;/,  goblet  cell;  g,  basement  membrane;  h,  tunica  propria;  i,  inner  circular 
layer  of  muscularis  mucosae;  k,  outer  longitudinal  layer  of  muscularis 
mucosae;  I,  inner  circular  layer  of  muscular  coat;  m,  outer  longitudinal 
layer  of  muscular  coat. 


Along  the  colon  and  the  first  part  of  the  rectum  the  serous  coat 
has  the  appendices  epiploicce  attached  to  it.  These  are  small  tabs 
of  adipose  tissue  that  vary  in  size  from  a  few  millimeters  to  a  centi- 
meter or  more.  Each  pad  of  adipose  tissue  is  covered  with  peri- 
toneum which  is  continuous  with  that  of  the  bowel  in  the  form  of 
a  delicate  pedicle.  The  fibers  in  this  adipose  tissue  do  not  respond 
well  to  the  ordinary  stains  and  give  a  hazy  picture  unlike  the  ordinary 
adipose  tissue.  At  times  leukocytes,  almost  in  sufficient  numbers  to 
constitute  diffuse  lymphoid  tissue,  are  found  in  the  adipose  tissue. 

The  rectum  has  its  mucous  and  submucous  coats  formed  into  folds 


2j6  PRACTICAL  HISTOLOGY 

called  the  rectal  valves.  These  contain  a  continuation  of  the  muscular 
coat,  by  means  of  which  the  valves  may  be  protruded  into  the  lumen. 
At  the  lower  end,  the  anus,  stratified  squamous  cells  replace  the  simple 
columnar,  and  this  marks  another  mucocutaneous  junction  as  in  the 
lips.  The  circular  libers  are  more  numerous  in  the  rectum  and 
especially  at  the  anal  extremity  where  they  form  the  internal  sphincter 
muscle.     This  is  about  4mm.  thick. 

The  appendix  is  a  continuation  of  the  cecum.  It  has  the  four 
coats,  mucosa,  submucosa,  muscularis  and  fibrosa,  or  serosa. 

The  mucosa  is  usually  irregular,  and  consists  of  simple  columnar 
epithelial  cells  that  rest  upon  a  basement  membrane)  beneath  the 
latter  lies  the  tunica  propria,  which  is  bounded  by  the  muscularis 
muscosce. 

In  the  mucosa  are  a  large  number  of  tube-like  depressions,  the 
glands  of  Lieberkiihn.  These  possess  an  equal  diameter  throughout, 
and  are  quite  regularly  distributed.  The  cells  of  the  mucosa  are  the 
simple  columnar  variety,  interspersed  with  many  goblet  cells.  They 
are  quite  distinct,  and  usually  possess  a  basal  border.  The  cells  in 
the  base  of  the  glands  supply -the  parts  higher  up,  and  are  conse- 
quently the  youngest.  The  glands  are  about  25,000  (Kelly  and 
Hurdon )  in  number,  and  are  absent  where  the  solitary  nodules  are 
found. 

The  tunica  propria  consists  of  a  delicate  nbro-elastic  stroma 
containing  many  capillaries,  considerable  diffuse  lymphoid  tissue  and 
solitary  nodules  (often  300  to  400  in  number).  The  solitary  nodules 
contain  germinal  centers,  and  may  extend  into  the  submucosa. 
Immediately  over  them,  the  glands  are  usually  absent. 

The  muscularis  mucosa  is  not  always  present.  It  consists  of 
smooth  muscle  fibers  forming  a  thin  band  separating  the  mucosa 
from  the  submucosa. 

The  submucosa  consists  of  loose  white  fibrous  tissue,  and  supports 
the  larger  blood-vessels.  In  older  subjects,  it  becomes  thicker  and 
denser,  and  passes  into  the  tunica  propria. 

The  muscular  coat  is  usually  separable  into  two  distinct  layers, 
inner  circular  and  outer  longitudinal.  The  former  is  the  more  prom- 
inent, and  extends  to  the  blind  end,  where  the  fibers  form  a  dome-like 
collection   of   interlacing  fibers.     The   longitudinal   fibers  are  less 


ALIMENTARY   TRACT 


277 


prominent  than  the  circular.  Both  layers  are  pierced,  at  intervals, 
by  large  vessels.  Such  an  opening,  of  which  one  especially  exists  at 
the  blind  end,  is  called  an  hiatus  (Kelly  and  Hurdon). 


Fig.  165. — Cross-section  of  Human  Appendix. 
a,  Lumen;  b,  epithelium;  c,  basement  membrane;  d,  glands;  e,  tunica  propria; 
/,    diffuse  lymphoid  tissue;   g,   muscularis  mucosas;   h,    solitary  nodule;   *, 
adipose   tissue;   k,    submucosa;    I,    circular   muscle   fibers;   m,    longitudinal 
muscle'fibers;  n,  fibrous  coat. 


The  serous  coat  consists  of  white  fibrous  tissue,  surrounded  by 
the  peritoneum. 

The  lumen  tends  to  disappear  more  frequently  than  supposed; 
this  change  occurs  during  the  ages  ranging  from  20  to  80.  The  older 
the   individuals,    the   higher    the   percentage   of   occlusions.     The 


278 


PRACTICAL  HISTOLOGY 


glands  are  gradually  destroyed  by  the  thickening  of  the  submucosa, 
this  process  beginning  at  the  blind  extremity  and  proceeding  toward 
the  bowel.  Occasionally,  in  this  process  of  occlusion,  quite  an 
abundance  of  adipose  tissue  is  seen  in  the  submucosa. 

The  blood-vessels  of  the  gastrointestinal  tract  pass  between  the 
layers  of  the  mesenteries,  or  omenta,  to  the  organs  where  the  large 
trunks  enter  the  submucous  coats.     In  the  case  of  the  stomach  the 


Fig.  166. — Section  of  the  Injected  Stomach  of  a  Guinea-pig. 
(Photograph.     Obj.  16  mm.,  oc.  75  X.) 


vessels  enter  from  along  the  curvatures  and  represent  branches 
from  the  aorta,  hepatic  and  splenic  arteries.  From  their  anasto- 
moses along  the  curvatures  main  trunks  enter  the  organ  and  in  passing 
through  the  muscle  coat  give  off  small  branches  thereto;  the  main 
vessels  continue  into  the  submucosa  where  they  anastomose  freely; 
from  this  plexus  branches  complete  the  supply  to  the  muscle  coat. 
Other  branches  pass  to  the  mucous  coat;  these  arterioles  are  at  first 
coiled  and  then  straight  giving  off  numerous  capillary  branches 
that  pass  between  the  glands  toward  the  epithelial  surface  where 


ALIMENTARY   TRACT 


279 


these  capillaries  form  a  coarse  meshwork  around  the  gastric  pits. 
From  this  plexus  the  venous  capillaries  form  a  fewer  number  of  larger 
venules  that  after  a  straight  course  between  the  glands  unite  near 
the  muscularis  mucosae  to  form  a  venous  plexus.     The  vessels  de- 


m. 

m.m. 
s.m. 

cm. 

i.c. 
l.m. 

s. 


» * . . .  --=>--  ------ 


ABC 

Fig.   167. — (Lewis  and  Stohr.) 

A,  Diagram  of  the  blood  vessels  of  the  small  intestine;  the  arteries  appear  as 
coarse  black  lines;  the  capillaries  as  fine  ones,  and  the  veins  are  shaded  (after 
Mall).  B,  Diagram  of  the  lymphatic  vessels  (after  Mall).  C,  Diagram  of 
the  nerves,  based  upon  Golgi  preparations  (after  Cajal).  The  layers  of  the 
intestine  are  m,.  mucosa;  m,  m.,  muscularis  mucosa?;  s.m.,  submucosa;  cm., 
circular  muscle;  i.e.,  intermuscular  connective  tissue;  l.m.,  longitudinal 
muscle;  s,  serosa.  c.L,  central  lymphatic,  n.  nodule,  s.pl.,  submucous 
plexus;  m.pl.,  myenteric  plexus. 


rived  from  this  plexus  pass  into  the  submucous  coat  where  they 
again  anastomose;  from  this  second  plexus  vessels  carry  the  venous 
blood  to  vessels  beneath  the  serous  coat  and  from  here  to  the  portal, 
splenic  and  superior  mesenteric  veins. 

In  the  small  intestine  the  terminal  loops  formed  by  the  branches 


280  PRACTICAL  HISTOLOGY 

of  the  superior  mesenteric  artery,  in  the  mesentery,  send  branches 
to  the  bowel;  these  branches  reach  the  organ  at  the  mesenteric 
attachment  and  each  usually  divides  into  two  that  separate  and 
encircle  the  bowel,  giving  off  branches  in  this  course  and  anasto- 
mosing after  the  circuit  is  completed.  These  vessels  lie  under  the 
serous  coat.  The  branches  ultimately  enter  the  submucosa,  sup- 
plying part  of  the  muscular  coat  on  the  way,  and  form  a  plexus  of 
vessels  in  the  submucosa;  branches  pass  to  the  muscular  and  mucous 
coats.  In  the  mucous  coat  another  plexus  is  formed  and  from  this 
numerous  capillaries  form  a  meshwork  around  the  glands  and  in- 
dividual capillaries  extend  straight  into  the  villi  to  their  tips,  forming 
a  meshwork  of  capillaries  just  beneath  the  basement  membrane. 
The  blood  continues  into  venules  that  start  near  the  tips  of  the  villi 
and  after  a  straight  course  through  the  mucosa  and  submucosa 
empty  into  the  submucous  plexus  of  veins.  This  plexus  receives 
also  the  blood,  through  venules,  from  the  deeper  (glandular)  portion 
of  the  mucosa  and  from  the  muscle  coat.  From  this  plexus  the 
efferent  vessels  have  a  course  corresponding  to  that  of  the  arteries. 

In  the  large  intestine,  owing  to  the  absence  of  villi,  the  vessels 
are  arranged  somewhat  as  in  the  stomach.  The  terminal  portion 
of  the  large  bowel  differs  though.  In  the  anal  end  of  the  rectum  the 
vessels  of  the  submucosa  are  longitudinally  arranged;  in  the  anal 
canal  they  lie  in  longitudinal  folds  of  the  mucosa.  The  veins  of 
these  parts  are  very  large  and  form  the  internal  and  external  hem- 
orrhoidal plexuses;  the  internal  plexus  has  for  its  efferent  vessel  the 
inferior  hemorrhoidal  vein  while  the  efferent  of  the  external  plexus 
is  the  superior  hemorrhoidal  vein. 

The  nerves  supplying  the  gastrointestinal  tract  are  the  two  vagi 
and  the  sympathetic  system.  These  nerves  form  two  great  plexuses, 
one  in  the  muscle  coat  and  the  other  in  the  submucous  coat;  at  the 
intersections  of  the  fibers  of  the  plexuses  there  are  sympathetic 
nerve  cells  in  greater  or  lesser  numbers  forming  large,  or  small 
terminal  ganglia. 

In  the  stomach  the  two  vagal  nerves  and  branches  from  the  solar 
sympathetic  plexus  are  the  sources  of  the  nerves.  These  enter  the 
organ  and  between  the  circular  and  longitudinal  muscle  layers  form 
the  myenteric  plexus  {plexus  of  Auerbach)  from  which  fibers  supply  the 


ALIMENTARY   TRACT  28 1 

muscle  fibers  of  this  coat.  Other  fibers  continue  into  the  submucous 
coat  where  they  form  the  submucous  plexus  (plexus  of  Meissner) 
from  which  branches  go  to  the  muscularis  mucosae  and  to  the 
epithelium  of  the  mucosa. 

In  the  small  intestine  the  nerve  fibers  that  form  the  corresponding 
plexuses  just  described  are  derived  from  the  right  vagal  nerve  and  the 
celiac  plexus  and  superior  mesenteric  ganglion.  These  nerves  at 
first  follow  the  larger  vessels  toward  the  intestine,  anastomosing 
with  one  another  in  this  course,  and  near  the  intestine  leave  these 
vessels  and  enter  the  walls  of  the  organ.  In  the  muscle  coat  the 
myenteric  plexus  is  formed  and  in  the  submucous  coat  the  submucous 
plexus  is  formed.  The  distribution  is  the  same  as  in  the  stomach 
except  the  villi  are  also  supplied,  some  of  the  fibers  going  to  the 
muscle  fibers  in  the  villi  and  others  to  the  epithelial  covering. 

In  the  large  intestine  the  nerve  fibers  are  mainly  from  the  second 
and  third  sacral  spinal  nerves  and  from  the  superior,  inferior  and 
hypogastric  plexuses  of  the  sympathetic  system.  These  nerves 
form  plexuses  that  are  distributed  in  the  foregoing  manner. 

The  numerous  lymph  spaces  of  the  stomach  surround  the  vessels 
and  glands.  The  lymph  capillaries  lie  in  the  mucosa  well  below  the 
surface  and  between  the  glands  and  receive  the  lymph  from  the  inter- 
cellular spaces.  At  the  region  of  the  muscularis  mucosae  these  cap- 
illaries form  a  plexus  the  efferents  of  which  pass  into  the  submucosa 
to  form  the  coarser  submucous  plexus,  the  vessels  of  which  possess 
valves.  Another  plexus  lies  between  the  muscle  coat  layers.  The 
efferents  from  these  two  plexuses  follow  the  blood-vessels  and  leave 
the  stomach  and  carry  the  lymph  to  nodes  around  the  stomach. 

In  the  small  intestine  the  intercellular  lymph  spaces  are  likewise 
extensive.  The  first  vessels  are  the  lacteals,  which  are  closed  at  the 
tips  of  the  villi  and  run  a  straight  course  toward  the  muscularis 
mucosae  where  they  all  terminate  in  the  mucous  plexus.  At  their 
junctions  with  the  plexus  the  lacteals  have  valves.  The  vessels  of 
the  mucous  plexus  are  mostly  valveless.  The  efferents  from  the 
mucous  plexus  carry  the  chyle  to  plexus  of  larger  vessels  in  the 
submucosa;  these  have  valves.  A  third  plexus  lies  between  the  layers 
of  the  muscle  coat.  Efferents  from  the  submucous  and  muscular 
plexuses  carry  the  lymph  to  the  fourth,  or  subserous  plexus,  which  is 


282 


PRACTICAL   HISTOLOGY 


most  prominent  at  the  mesenteric  attachment.  The  efferents  from 
the  subserous  plexus  follow  the  vessels  and  in  the  mesentery,  at 
frequent  intervals,  the  chyle  is  filtered  through  numerous  lymph 
nodes  before  it  ultimately  reaches  the  common  intestinal  trunk. 

The  cells  lining  the  various  portions  of  the  alimentary  tract  are 
as  follows: 

Lips Stratified  squamous. 

Mouth Stratified  squamous. 

Tongue Stratified  squamous. 

Pharynx Stratified  squamous 

Esophagus Stratified  squamous 

Acid  cells. 

Peptic  cells. 

Tall  columnar. 

,  Goblet  cells  (a  few). 

Peptic  cells. 

Tall  columnar 

Goblet  cells. 

Simple  columnar. 
.  Goblet  cells. 

Large  intestine J  Goblet  cells. 

1  Simple  columnar. 
Anus Stratified  squamous. 


Stomach 


Cardiac  end. 


Pyloric  end  . 


Small  intestine. 


The  differences  between  the  small  and  large  intestines  are  as 

follows: 

Small.  Large. 

Glands.                                     Long  and  narrow.  Broad. 

Cells.                                        Chiefly  Chieply 

glandular.  goblet. 

Present.  Absent. 

Present.  Absent. 

Present.  Absent. 

Present.  Absent. 

Absent.  Present. 


Villi. 
Plioe. 

Brunner's  glands 
Peyer's  patches. 
Longitudinal 

bands. 
Sacculations. 


Absent 


Present, 


CHAPTER  X 

THE  DIGESTIVE  GLANDS 

The  digestive  glands  are  the  liver,  and  salivary  glands,  the 
parotid,  pancreas,  sublingual  and  submaxillary. 

LIVER 

The  liver,  the  largest  gland  in  the  body,  is  compound  tubular  in 
structure.  In  the  child  at  birth  it  represents  one-eighteenth  to 
one-twentieth  of  the  body  weight,  while  in  the  adult  it  represents 
about  one-fortieth,  weighing  from  48  to  58  ounces  in  the  male  and 
45  to  50  ounces  in  the  female.  It  is  surrounded  by  a  sheath  of 
white  fibrous  tissue,  the  capsule  of  Glisson,  which  is  covered  by 
peritoneum.  On  the  under  surface  of  the  organ,  the  capsule  follows 
the  blood-vessels  at  the  portal  or  transverse  fissure  into  the  gland, 
and  forms  the  interlobular  connective  tissue  and  intralobular  reticulum. 
Folds  and  bands  form  the  various  ligaments,  suspensory,  coronary 
and  lateral.  The  round  ligament  is  formed  by  the  persistent,  closed 
umbilical  vein. 

The  liver  is  divided  into  lobes  and  lobules,  of  which  the  latter 
represent  the  units.  A  description  of  a  lobule  will  suffice  for  that 
of  the  whole  liver. 

Each  lobule  is  about  1  mm.  in  diameter  and  Mall  states  that 
there  are  about  480,000  in  the  liver.  Each  consists  of  a  collection  of 
anastomosing  and  radiating  chains  of  hepatic  cells,  the  tubules, 
that  start  from  the  central,  or  intralobular  vein,  which  represents 
a  large  sinusoid.  These  chains  are  separated  from  one  another 
by  reticulum,  which  supports  the  cells  and  the  intralobular  blood 
capillaries;  these  capillaries  are  of  the  sinusoidal  variety;  that  is, 
the  endothelium  is  attached  to  the  epithelium  of  the  tubules.  As 
a  result  the  material  for  secretion  is  transferred  directly  from  the 
blood  to  the  liver  cells  and  the  internal  secretion  is  transferred 

283 


284 


PRACTICAL  HISTOLOGY 


directly  from  the  cells  to  the  blood  without  the  intervention  of  the 
lymph  or  lymph  vessels.  Each  chain  consists  of  two  or  three  cells 
side  by  side,  enclosing  a  small  capillary  space  called  the  bile  capillary. 
Peripherally,  the  lobules  are  not  separated  from  one  another  by 
connective  tissue,  except  in  the  pig  and  camel.  In  these  animals, 
the  lobules  are  sharply  outlined  by  bands  of  connective  tissue.  This 
occurs  somewhat  imperfectly  in  the  human  liver  under  pathologic 
conditions  (chronic  interstitial  hepatitis). 


Fig.  168. — Section  of  a  Lobule  of  the  Human  Liver. 
c,   Central  vein.     (Photograph.     Obj.  16  mm.,  oc.  5  X.) 

According  to  Mall,  the  lobule,  as  now  considered,  is  not  the 
structural  unit  of  the  liver;  the  structural  unit  refers  to  all  the  tissue 
that  surrounds  each  terminal  branch  of  the  portal  vein. 

From  the  capsule  of  Glisson  large  bands  or  trabecular  pass  into  the 
organ  forming  the  coarse  framework  of  the  liver  and  supporting 
the  larger  vessels,  ducts  and  nerves.  From  the  interlobular  tra- 
becular the  intralobular  reticulum  is  derived.  This  is  a  very  delicate 
meshwork  of  fine  fibrils  that  support  the  functionating  hepatic 
cells  and  the  intralobular  capillaries.  Owing  to  the  fineness  of  the 
reticulum,    but    especially    to    the    extremely    close    relation    of 


THE   DIGESTIVE    GLANDS 


285 


True  meshes. 


Lateral  branches  of  bile  capillaries. 


Sinusoids.  Portion  of  a  central  vein. 

Fig.   169. — From  a  Cross-section  of^a  Human    Hepatic  Lobule.      x  300. 

(Lewis  and  Stohr.) 

Golgi  preparation.  The  boundaries  of  the  hepatic  cells  could  not  be  seen.  The 
black  dots  are  precipitates  of  the  silver.  I,  Bile  capillary  in  the  ansatomosis 
between  two  hepatic  trabecular;  2,  nucleus  of  an  endothelial  cell  of  a  sin- 
usoid; 3,  nucleus  of  an  hepatic  cell;  4,  nuclei  of  hepatic  cells. 


286 


PRACTICAL  HISTOLOGY 


the  blood  capillaries  and  the  epithelial  cells  this  reticulum 
is  practically  invisible  or  hidden  in  the  ordinary  section  10 
microns  thick.  In  order  to  see  it  it  is  best  to  prepare  digested 
preparations.  In  special  preparations  stellate  cells  with  two  or 
three  processes  are  seen  in  the  lobules.  These  are  the  cells  of 
Kupfer.  These  cells  may  have  one  or  two  nuclei;  they  are  uniformly 
distributed  in  the  lobule  and  are  said  to  be  phagocytic.  In  certain 
regions,  at  the  junctions  of  several  lobules,  large  masses  of  the 


^ 


Fig.  170. — Reticulum  of  a  Liver  Lobule. 
c,   Central  vein;  i,  interlobular  area.     (Schafer  after  Oppel.) 


interlobular  connective  tissue  are  seen.  Upon  examination  these 
masses  usually  contain  a  branch  of  the  portal  vein,  hepatic  artery, 
hepatic  vein  and  bile  duct  and  are  called  the  portal  canals,  or  systems. 
In  pigs  and  camels  the  interlobular  connective  tissue  is  so  abundant 
as  to  form  a  complete  investment  of  each  lobule,  so  that  in  sections, 
each  lobule  is  separated  from  its  neighbor  by  a  complete  wall  of 
white  fibrous  tissue.  The  portal  canals  are  present  here  as  above. 
The  hepatic  cells  are  large  mononuclear  masses  of  protoplasm; 
occasionally  two  nuclei  may  be  present  in  one  cell.     The  cytoplasm 


THE   DIGESTIVE    GLANDS 


287 


is  finely  granular  and  an  exoplasmic  zone  may  be  differentiated. 
These  cells  are  traversed  by  a  network  of  line  canals,  the  secretory 
capillaries,  that  may  communicate,  on  the  one  hand,  with  the  bile 
capillaries  between  the  cells,  or  on  the  other  hand,  with  the  sinu- 
soidal blood  capillaries  that  surround  the  epithelial  cells.  It  has 
been  shown  that  these  capillaries  extend  to  the  periphery  of  the 
hepatic  cell  and  are  in  such  close  relation  with  the  sinusoid  that 
the  internal  secretions  of  the  liver  (from  its  glycogenic  and  urea- 
forming  functions)  are  readily  poured  into  the  blood-vessels. 

One  of  the  important  functions  of  the  liver  is  that  of  forming 
glycogen  and  storing  it  until  it  is  required.     This  substance  is  in 


ds  pa 


Fig.  171. — Intracellular  Canaliculi  of  the  Liver  Cells  Communicating 
with  the  Sinusoid.     (After  Schafer.) 


the  form  of  granules  of  different  sizes  and  the  quantity  present 
varies  at  different  times.  After  meals  rich  in  carbohydrates  the 
glycogen  in  great  in  quantity;  after  meals  poor  in  these  substances 
there  is  less.  After  periods  of  abstinence  from  carbohydrates 
glycogen  is  almost  absent  from  the  liver  cells.  It  can  readily  be 
demonstrated  by  means  of  special  stains.  It  is  readily  soluble  in 
water  and  dilute  alcohols  so  that  strong  alcohol  is  one  of  the  best 
fixing  agents  for  its  demonstration. 

A  few  fat  globules  are  normal  in  hepatic  cells;  these  are  usually 
small  in  size  and  are  distributed  mainly  in  those  cells  at  the  periphery 
of  the  lobule.     After  a  meal  rich  in  fatty  foods  the  number  of  fat 


288  PRACTICAL  HISTOLOGY 

globules  is  greatly  increased.  If  large  quantities  of  fat-forming 
foods  are  constantly  taken  then  fat  is  found  in  abundance  in  all  of 
the  cells.  The  fat  globules  usually  coalesce  to  form  one  or  more 
large  droplets  and  the  condition  is  that  of  fatty  infiltration.  In 
fatty  degeneration  of  the  liver  cells  the  fat  globules  are  numerous 
but  small  in  the  degenerating  cells  and  they  do  not  coalesce.  Fat 
may  be  readily  demonstrated  by  means  of  osmic  acid  solutions  or 
any  other  special  stain  for  fat. 

Pigment  granules  are  often  found  in  hepatic  cells  especially  those 
near  the  central  vein.  This  is  an  iron  pigment  and  is  present 
in  the  form  of  small  granules  that  are  not  numerous  in  normal 
conditions.     Mitochondria  are  also  found  in  hepatic  cells. 

The  bile  capillaries  that  lie  between  the  cells  of  the  tubules  or 
chains,  are  merely  notches  in  the  opposed  cells  and  start  blindly 
near  the  central  vein.  These  capillaries  are  small  and  some  con- 
sider them  true  secretory  capillaries.  They  correspond,  however, 
to  the  lumen  of  the  alveolar  or  ordinary  tubular  glands  but  differ 
in  the  fact  that  they  form  an  anastomosing  set  of  capillaries  through- 
out the  entire  lobule  and  do  not  empty  into  intralobular  ducts  as 
there  are  no  such  ducts  present  in  the  liver.  In  some  instances 
three  cells  form  the  chains  and  all  participate  in  the  formation  of 
the  capillary;  in  the  frog  five  cells  are  said  to  form  the  tubules  and 
then  each  one  would  participate  in  the  formation  of  this  channel. 
At  the  periphery  of  the  lobule  these  capillaries  empty  into  the  deli- 
cate interlobular  ducts.  The  first  of  these  ducts  consists  of  a  lining 
of  low  columnar  epithelial  cells  that  rest  upon  a  delicate  basement 
membrane  that  is  supported  by  a  small  amount  of  areolar  tissue, 
the  tunica  propria.  These  soon  join  larger  ducts  that  lie  in  the 
interlobular  tissue  and  receive  the  bile  from  a  considerable  area; 
these  larger  duels  have  three  coals  and  are  lined  with  tall  columnar 
cells  that  rest  upon  a  delicate  basement  membrane  and  tunica 
propria;  outside  of  this  is  a  muscle  coal  consisting  of  circularly 
arranged  smooth  muscle  tissue  supported  by  the  fibrous  coat. 
These  ducts  are  the  ones  noted  in  the  portal  canals.  The  largest 
ducts  have  the  same  general  structure  and  goblet  cells  may  be  found 
in  the  epithelial  layer;  the  muscle  coat  is  usually  thicker  and  more 
prominent.     The  ducts  of  the  right  and  left  lobes  join  to  form  the 


THE   DIGESTIVE   GLANDS 


289 


right  and  left  lobar  ducts,  respectively,  and  the  structure  of  these  is 
similar  to  that  of  the  hepatic  and  cystic  ducts. 

The  circulation  of  the  liver  is  more  peculiar  and  interesting  than 
that  of  any  other  organ  in  the  body.     Two  systems  bring  blood, 


Fig.  172. — Liver  of  Pig. 
a,  Interlobular  connective^tissue  containing  a  portal  system  consisting  of 

Ib,    Interlobular  branch  of  hepatic  artery. 
c,    Interlobular  branch  of  portal  vein. 
d.   Interlobular  branch  of  bile  duct. 
e,  chains  of  hepatic  cells;  /,  central  vein;  g,  chain  of  cells  highly  magnified. 

yet  it  leaves  through  one.     In  other  organs,  the  vessel  that  supplies 
the  functionating  tissue  is  an  artery,  but  here  it  is  a  vein,  the  portal 

19 


290 


PRACTICAL  HISTOLOGY 


vein.     According  to  Pearce  the  portal  vein  furnishes  about  60  per 
cent,  of  the  blood  and  the  hepatic  artery  about  30  per  cent. 

The  portal  vein  is  made  up  of  the  superior  and  inferior  mesenteries, 
coronary   (stomach)   and  splenic  veins.     This  blood  represents  the 

venous  return  from  the  gastrointes- 
tinal tract.  It  is  richly  laden  with 
the  altered  carbohydrates  and  digested 
proteins  but  contains  little  fat.  It 
enters  at  the  portal  or  transverse  fissure 
of  the  liver,  and  forms  two  main 
branches,  right  and  left,  one  for  each 
main  lobe.  These  rapidly  form  in- 
terlobular branches  that  give  rise  to 
the  intralobular  capillaries,  found  in 
the  lobules,  where  they  converge  at 
the  center  and  empty  into  the  central, 
or  intralobular  vein. 

The  hepatic  artery  enters  the  trans- 
verse fissure,  and  forms  lobar  and 
interlobular  branches.  The  latter 
rapidly  form  capillaries  that  He  in  the 
interlobular  connective  tissue  and 
nourish  it,  and  the  vessels  found 
here.  These  are  the  interlobular 
capillaries,  some  of  which  enter  the 
outer  third  of  the  lobule  and  empty 
into  the  portal  vein  capillaries.  The 
remainder  of  the  hepatic  artery  capil- 
laries empty  into  the  interlobular  branch  of  the  portal  vein,  or  form 
small  venules  that  ultimately  empty  into  these. 

The  blood  that  has  entered  the  central  vein,  from  the  portal  vein 
and  the  hepatic  artery,  passes  into  the  sublobular  veins,  which  are 
formed  by  a  union  of  the  centrals,  and  then  into  the  interlobular 
branches  of  the  hepatic  veins.  The  interlobulars  are  formed  by  a 
union  of  the  sublobulars,  and  these,  in  turn,  unite  to  form  the 
hepatic  veins  that  empty  into  the  blood  the  postcava,  or  inferior 
vena  cava. 


Fig.  173. — Terminal  Branches 
of  the  Hepatic  Artery 
Forming     a     Capillary 

Meshwork. 

P,  Branch  of  portal  vein;  H, 
branch  of  hepatic  artery. 
(After  Mall.) 


THE  DIGESTIVE   GLANDS 
The  circulation  of  the  liver  might  be  outlined  as  follows: 


291 


Portal  vein 

i 
Lobar  branches. 

i 
Interlobular  veins. 


Hepatic  artery. 

i 
Lobar  branches. 

i  . 

Interlobular  arteries. 

1 
Interlobular   capillaries. 


Intralobular  capillaries 


Central  vein. 

1 
Sublobular  vein. 

Interlobular  vein. 

i. 
Hepatic  veins. 

As  the  portal  vein  blood  comes  into  intimate  relation  with  the 
hepatic  cells,  the  latter  remove  the  products  required  for  nutrition, 
also  the  excess  of  glucose,  which  is  converted  into  liver  sugar,  or 
glycogen,  and,  in  addition,  take  out  the  constituents  of  the  bile;  it  is 
now  considered  the  seat  of  urea  formation. 

The  lymphatics  are  superficial  and  deep.  The  superficial  drain 
into  either  the  celiac  and  hepatic  lymph  nodes  on  the  one  hand,  or 
through  the  diaphragm  into  the  ventral  mediastinal  nodes.  The 
deep  pass  out  either  through  the  portal  fissure  to  hepatic  and  celiac 
nodes,  or  along  the  hepatic  vein  pass  through  the  diaphragm  to  nodes 
around  the  postcava.  The  blood-vessels  are  surrounded  by  lymph 
spaces  that  communicate  with  similar  spaces  at  the  periphery  of  the 
lobule  and  in  the  interlobular  connective  tissue.  Within^the  lobule 
lymph  spaces  are  not  numerous  as  the  endothelial  cells  of  the 


292 


PRACTICAL  HISTOLOGY 


sinusoids  are  attached  to  the  epithelial  cells  of  the  hepatic  tubules. 
In  the  interlobular  area  the  lymph  spaces  and  channels  are  numerous 
and  the  lymph  is  abundant. 

The  sympathetic  nerves  form  the  chief  source  of  enervation  of  the 
liver.     They  lie  in  the  interlobular  connective  tissue  as  plexuses, 


H  P 

Fig.   174. — Terminal  Branches  of  the  Veins  of  the  Liver. 
H,   Branch    of   hepatic    vein;    P,  branch    of    the    portal    vein;  S,    sublobular 
vein;  C,  central    vein;  i,  interlobular  branch   of    the  portal  vein.      (After 
Mall.) 


and  from  these  some  fibers  pass  to  the  bile  ducts,  and  blood-vessels 
and  others  penetrate  the  lobules  to  pass  beneath  the  cells.  Here 
they  are  said  to  end  upon  the  epithelial  cells  as  knobs  or  fibrils. 

The  excretory  apparatus  consists  of  the  gall-bladder,  hepatic 
cystic  and  common  ducts.  They  all  possess  three  coats,  mucous, 
muscular  and  fibrous. 


THE   DIGESTIVE   GLANDS 


293 


The  hepatic  duct  is  about  2.5  to  3  cm.  in  length  and  3  to  4  mm.  in 
diameter;  the  cystic  duct  is  about  3  to  3.75  cm.  in  length  and  3  to 
4  mm.  in  diameter;  the  ductus  cholidochus  is  about  8.5  to  10  cm.  in 
length  and  to  6  to  7  mm.  in  diameter.  These  are  alike  in  structure. 
The  mucous  coat  consists  of  a  single  layer  of  tall  columnar  and  goblet 
cells  that  rest  upon  a  basement  membrane  and  tunica  propria.     In  the 


Fig.   175. — Cross-section  of  the  Hepatic  Duct. 

a,  a,   Tubules  of  glands;   b,   areolar  tissue;   m,  m,   smooth  muscle  tissue  of  muscle 
coat;  L,   lumen  of  the  duct.      (After  v.  Ebner.) 


latter  are  seen  a  number  of  tubulo alveolar  glands  that  open  out  upon 
the  epithelial  surface.  Diverticula  of  the  mucosa  are  also  numerous 
especially  in  the  hepatic  duct  and  even  within  the  liver  substance. 
The  muscle  fibers  are  quite  distinct.  They  are  arranged  as  circular, 
longitudinal  and  oblique  layers.  The  circular  fibers  of  the  common 
duct  form  a  sphincter  at  its  entrance  into  the  duodenum.  This  is 
supported  by  a  rather  thick  layer  of  white  fibrous  tissue  constituting 
the  fibrous  coat. 


294 


PRACTICAL   HISTOLOGY 


The  mucosa  of  the  gall-bladder  consists  of  tall  columnar  and  goblet 
cells,  basement  membrane  and  fibro-elastic  tunica  propria.  The 
epithelial  cells  resemble  those  of  the  small  intestine  and  secrete 
mucous.  The  tunica  propria  contains  a  few  mucous  glands,  some 
diffuse  lymphoid  tissue  and  even  solitary  nodules  and  some  muscle 
fibers  derived  from  the  muscle  coat.  In  the  empty  and  partially 
distended  condition  the  mucosa  is  seen  formed  into  rugous  folds, 
which  at  the  neck  are  permanent. 

The  muscle  coat  is  composed  of  smooth  muscle  tissue  and  a  con- 
siderable quantity  of  white  fibrous  tissue,  the  latter  predominating 


Epithelium. 


Muscularis. 


Tunica 
propria 


Cuticala. 


A  B 

Fig.   176. — From  a  Section"  of  the  Gall-bladder  of  an  Adult,  A. 
B,   The  portion  x  of  A.       X  560.      (Lewis  and  S to hr.) 


X  100. 


near  the  mucous  coat.  Elastic  tissue  is  also  present.  The  muscle 
fibers  interlace  somewhat  although  most  of  them  are  circularly 
arranged.  The  fibrous  coat  consists  of  white  fibrous  tissue  that  is 
attached  to  and  connected  with  the  fibrous  tissue  of  the  liver. 
It  is  partially  invested  with  the  peritoneum. 

The  lymphatics  are  connected  to  those  of  the  liver  by  the  subserous 
plexus,  into  which  the  vessels  from  the  muscular  coat  empty. 

The  nerves  are  sympathetic  and  cerebrospinal,  the  former  passing 
to  the[blood- vessels  and  muscles,  and  the  fatter-ending  in  the  mucosa, 
near  large  arteries.  Sympathetic  ganglia,  also,  are  found  in  the 
walls  of  the  gall-bladder  and  nerve  fibers  and  free  sensory  organs  are 
found  in  the  epithelial  layer. 


THE   DIGESTIVE    GLANDS 
SALIVARY  GLANDS 


295 


The  salivary  glands  are  the  parotid,  pancreas  (the  abdominal 
salivary  gland),  sublingual  and  submaxillary  glands.  In  addition, 
there  are'a  large  number  of  small  unnamed  glands  in  the  lips,  mouth, 
tongue,  pharynx,  base  of  the  epiglottis,  palate  and  esophagus. 

According  to  secretion,  they  are  divided  into  mucous,  serous  and 
mixed. 


*& 


Fig.  177. — Interstitial  Tissue  of  the  Human  Sublingual  Gland. 

a,   Artery;   d,   duct;   v,  vein;  i,   interlobular  connective  tissue;   m,   mucous  lob' 

ule;  it,  n,  interlobular  septa;  s,   serous  lobule.     (/.  M.  Flint.) 


The  mucous  glands  are  distinguished  by  their  large  secretory  units 
that  stain  lightly.  These  are  the  acini,  alveloi  or  tubules,  and  they 
give  rise  to  a  thick  viscid  secretion.  Such  glands  are  the  small  glands 
of  the  mouth,  pharynx  and  esophagus.  The  sublingual  is  almost  a 
pure  mucous  gland. 

Serous  glands  are  those  in  which  the  acini  stain  darkly,  owing  to 
the  presence  of  secretory  granules  in  the  cytoplasm,  which  retain 
the  stain.     The  acini  are  usually  smaller  than  those  of  mucous  glands 


296  PRACTICAL   HISTOLOGY 

These  glands  secrete  a  thin  albuminous  fluid.     Such  are  the  parotid 
and  pancreas. 

The  mixed  glands  are  those  that  stain  both  lightly  and  darkly, 
and  secrete  a  mixed  fluid,  as  the  submaxillary  and  sublingual. 

As  all  of  these  glands  have  the  same  general  structure,  this  will  be 
first  considered,  and  the  special  points  then  noted. 

Each  is  surrounded  by  a  capsule  of  white  fibrous  tissue  that  limits 
it  from  the  surrounding  organs  or  tissues.  The  capsule  sends  in 
prolongations  that  divide  the  gland  into  lobes  and  lobules.  The 
lobules,  or  structural  units,  consist  of  the  functionating  units  that  are 
composed  of  a  single  layer  of  glandular  epithelial  cells  {parenchyma) 
supported  by  a  basement  membrane.  External  to  the  basement 
membrane,  is  the  interstital,  or  intertubular  connective  tissue,  which 
is  composed  of  reticulum,  and  in  which  the  blood-vessels,  nerves  and 
lympathatics  are  found.  It  corresponds  to  the  tunica  propria  of  a 
mucous  membrane. 

The  secretory  units  lead  into  minute  intermediate,  or  intercalated 
tubules  that  unite  to  form  intralobular  ducts,  which  pass  into  the 
interlobular  connective  tissue.  Here  they  unite  to  form  the  inter- 
lobular ducts ;  these,  by  union,  form  the  lobars,  and  then  the  single 
excretory  duct.  The  intermediate  tubules  are  lined  by  simple 
squamous  or  low  columnar  cells,  supported  by  basement  membrane 
and  interstitial  tissue;  the  interlobular  branches  contain  simple 
columnars,  the  intralobular  and  interlobars  are  lined  by  pseudo- 
stratified  columnars,  and  the  excretory  duct  usually  by  stratified 
columnars.     In  the  latter  duct  the  muscle  coat  is  distinct. 

The  blood-vessels  follow  the  divisions  of  the  ducts,  and  form 
plexuses  of  capillaries  around  the  secretory  units,  and  in  close  prox- 
imity to  the  epithelium. 

The  nerves  pass  down  in  the  same  manner,  and,  after  penetrating 
the  basement  membrane,  end  around  the  cells. 

The  parotid  gland  is  a  compound  alveolar  gland  and  is  divided 
into  lobes  and  lobules  as  has  been  described.  It  represents  the 
largest  oral  salivary  gland.  In  each  lobule  are  seen  the  secreting 
units,  or  acini,  which  are  serous  in  character,  the  intercalated  and 
intralobular  ducts.  Each  acinus  consists  of  a  number  of  small 
darkly  staining  cells  of  a  pyramidal  shape  arranged  in  a  single  layer 


THE   DIGESTIVE    GLANDS  297 

upon  the  thin  basement  membrane.  In  the  center  of  the  group  of 
cells  is  a  lumen,  the  size  of  which  depends  upon  the  stage  of  activity 
of  the  gland.  The  acini  are  comparatively  small.  The  basement 
membrane  contains  flattened  basket  cells  at  the  bases  of  the  epithelial 
cells,  and  the  processes  of  these  basket  cells  pass  between  the  func- 
tionating epithelium.  These  are  supposed  to  be  young  secreting 
cells  that  replace  the  older  ones  as  they  give  out.  The  cytoplasm  of 
the  secreting  cells  is  nearly  clear  and  finely  granular  in  the  early  rest- 
ing stage;  during  the  latter  part  the  granules  increase  in  number  and 
a  small  amount  of  clear  cytoplasm  and  the  nucleus  occupy  the  basal 
portion  of  the  cell.  The  cell  becomes  so  swollen  as  to  occlude  the 
lumen  and  as  these  zymogen  granules  are  discharged  during  the  active 
stage  the  cells  become  smaller  and  the  granules  nearly  all  disappear; 
the  clear  cytoplasm  increases  in  amount  and  spreads  through  the 
cell.  Prozymogen,  or  mitochondrial  filaments  have  been  demonstrated 
in  the  basal  portion  of  the  cells.  In  the  cytoplasm  and  between 
the  cells  there  is  a  set  of  secretory  capillaries,  or  canaliculi.  The 
acini  pass  the  secretion  to  the  intercalated  tubules  that  are  lined  with 
squamous  cells  and  these  join  the  intralobular  ducts  that  are  lined 
with  low  columnar  elements.  These  in  turn  empty  into  the  in- 
terlobular ducts  that  lie  in  the  interlobular  connective  tissue.  These 
are  larger  in  caliber  and  are  lined  with  columnar  cells  and  possess 
three  coats. 

Considerable  adipose  tissue  is  found  in  the  interlobular  tissue  of 
the  parotid  gland. 

The  parotid  duct  is  the  excretory  duct. 

The  pancreas  is  the  other  serous  gland  and  is  compound  alveolar 
in  structure.  It  is  also  called  the  abdominal  salivary  gland.  Its 
general  structure  is  analagous  to  that  of  the  parotid.  The  lobules 
contain  the  secreting  units,  or  acini  that  are  larger  than  those  of  the 
parotid  however.  These  acini  are  usually  distinct,  sharply  outlined 
and  stain  darkly.  Here  and  there  between  them  are  seen  the  is- 
lands of  Langerhans  that  will  be  described  later.  The  cells  lining  an 
acinus  are  of  the  pyramidal  type  and  the  amount  of  lumen  showing 
will  depend  upon  the  stage  of  secretory  activity.  These  cells  rest 
upon  the  basement  membrane  but  interposed  are  the  peculiar  stellate 
basket  cells  that  are  immature  secreting  cells,  so  it  is  said.     During 


298  PRACTICAL  HISTOLOGY 

rest  these  cells  show  a  clear  cytoplasm,  only  a  few  granules  being 
present  near  the  lumen  end.  As  the  secretion  is  being  formed  these 
zymogen  granules  increase  in  amount,  the  cell  becomes  swollen  and 
only  a  narrow  rim  of  cytoplasm,  containing  the  nucleus,  is  seen  at 
the  basal  portion  of  the  cell.  The  lumen  is  practically  occluded. 
With  the  discharge  of  the  secretion  the  clear  cytoplasm  increases  and 
spreads  through  the  cell,  which  is  much  smaller  in  size.     The  nucleus 


Fig.  178. — Section  of  Human  Pancreas  showing  Pancreatic  Islands. 
a,   Interlobular  connective  tissue;   b,   capillary;   c,   interlobular  duct;   d,   intra- 
lobular duct;  c,  cells  of  acini;  /,  area  of  Langerhans. 

plays  an  important  part  in  secretion.  A  paranucleus  is  seen  in  active 
cells.  This  is  derived  from  extruded  nuclear  material  and  is  said 
to  be  changed  into  secretion  granules  but  this  is  denied  by  some. 
In  the  basal  portions  of  the  cells  mitochondrial  filaments  are  readily 
demonstrated.  These  are  said,  by  some,  to  give  rise  to  the  zymogen 
granules,  but  others  believe  that  they  are  concerned  only  with  the 
metabolic  activities  of  the  cell.  Within  many  of  the  acini  are  seen 
lightly  staining  flattened  elements  that  are  called  the  centro-ocinar 
cells.     These  are  characteristic  of  the  pancreas  and  represent  the 


THE   DIGESTIVE   GLANDS 


299 


squamous  cells  of  the  intercalated  tubules  invaginated  into  the  acinus. 
They  are  separated  from  the  secreting  cells  by  intercellular  secretory 
capillaries. 

In  addition  to  the  acini  numerous  groups  of  lightly  staining  cells 
are  scattered  in  the  lobules;  these  are  the  pancreatic  islands,  or 
areas  of  Langerhans.  These  are  oval,  or  circular  in  outline  and  each 
is  surrounded^by  a  delicate  capsule  that  sends  in  trabecular  that  seem 
to  arrange  the  cells  into  irregular  groups,  or  cords.     The  number  of 


Blood 
capillary. 


Cells  of 
the  al- 
veolus. 


Centro-alveolar  cells. 


Zymogen  granules. 


A  B 

Fig.  179. — From  Sections  of  a  Human  Pancreas,    x  500.     {Lewis  and  Stohr.) 
In  section  A  the  granules  are  wanting,  the  centro-alveolar  cells  are  flat  and  dark; 

in  section  B  the  granules  are  distinct,  the  centro-alveolar  cells  are  cuboidal 

and  clear. 


cells  in  an  island  varies  from  several  to  many  so  that  these  islands 
may  be  microscopic  or  macroscopic  (3  mm.)  in  size.  The  cytoplasm 
of  these  cells  stains  lightly  and  contains  some  fine  eosinophilic 
granules  that  are  supposed  to  be  of  two  kinds  and  therefore  form  two 
different  kinds  of  secretion.  The  blood-vessels  are  of  the  sinusoidal 
type  and  are  in  close  relation  to  the  cells,  forming  glomerule-like 
masses  in  injected  sections.  These  possess  no  outlet  for  the  secre- 
tion {enzyme,  or  harmone)  that  they  form  and  this  is  supposed  to  be 
passed  directly  to  the  blood  capillaries. 

These  islands  are  most  numerous  in  the  splenic  end  of  the  pancreas 
and  vary  considerably  in  number.     Dole  states  that  they  may  be 


3°° 


PRACTICAL   HISTOLOGY 


increased  in  size  and  number  by  means  of  secretion  and  that  in  long 
hunger  they  are  also  increased;  this  probably  merely  represents  a 
normal  individual  variation.  Thompson  and  others  claim  that  there 
is  a  connection  or  lumen  between  the  islands  and  acini  in  reptiles 
and  fishes.  This  connection  does  not  apparently  exist  in  man  as 
ligation  of  the  pancreatic  duct  does  not  affect  the  islands  nor  does 
it  interfere  with  carbohydrate  metabolism.  If  the  islands  are  dis- 
eased (in  some  cases  at  least)  or  if  the  pancreas  of  an  animal  be  re- 
moved diabetes  mellitus  follows.  The  areas  then,  postmortem,  show 
degenerative  changes. 


Inter-  Centro-alveolar  cells. 

calated  Cells  of  the 

duct.       \  i  .      alveolus 


Intercellular 
secretory  „ 
capiHary.  A  B 

Fig.  180. — A,  From  a  Section*  of  the  Pancreas  of  an  Adult  Man.  x  320. 
B.  An  Interpretation  of  the  Right  Lower  Portion  of^.  (Lewis  and 
Stohr.) 


According  to  Bensley  some  of  these  islands  may  be  found  in  the 
interlobular  tissues  connected  with  the  ducts;  some  in  the  lobules 
connected  with  the  ducts;  other  in  the  lobules  connected  with  the 
ducts  and  acini;  others  not  connected  with  the  ducts  or  the  acini. 
Although  the  acini  and  the  islands  seem  to  have  the  same  origin  in 
the  embryo,  after  their  adult  stage  they  are  unalterable.  They  may 
be  stained  intravitam  by  means  of  neutral  red  and  janus  green. 

The  excretory  duct,  the  duct  of  Wirsung,  is  lined  by  simple  col- 
umnar cells. 

The  submaxillary  gland  is  a  tubuloalveolar  gland  in  structure  and 
a  mixed  gland  in  secretion.  The  mucous  tubules  may  be  collected 
in  individual  lobules  and  lobes  or  they  may  be  mixed  with  the  serous 
acini.     In  man  it  is  said  that  the  serous  acini  are  five  times  as  nu- 


THE   DIGESTIVE   GLANDS 


301 


merous  as  the  mucous  tubules.  The  serous  acini  resemble  in  struc- 
ture those  of  the  preceding  glands  and  the  acini  are  intermediate  in 
size  between  those  of  the  parotid  and  pancreas.  The  mucous  tub- 
ules are  the  larger.  The  cells  are  of  the  column  variety,  are  quite 
large  and  stain  lightly.  In  the  fresh  condition  the  cytoplasm  is 
clear  and  refractile.  In  properly  fixed  tissue  the  cytoplasm  contains 
a  coarse  reticulum  that  is  basophilic  in  reaction  and  is  located  mainly 
in    the   lumen   portion   of   the   cell.     The   cytoreticulum   contains 


Fig.  181. — Area  of  Langerhans  of  the  Injected  Pancreas  of  a  Guinea-pig. 
(Photograph.     Obj.  16  mm.,  oc.  7.5    X.) 

some  coarse  granules  that  respond  to  special  mucin  stains.  During 
the  resting  stage  these  granules  increase  in  number  and  the  cells  be- 
come larger  and  have  a  swollen  appearance.  When  the  secretion 
is  to  be  discharged  water  from  the  lymph  between  the  cells  passes 
into  the  cells,  the  granules  swell  and  are  dissolved  and  the  secretion 
is  discharged.  The  cell  is  then  smaller.  These  granules  do  not 
show  in  ordinary  preparations  as  they  are  so  soluble  that  they  must 
be  fixed  in  certain  reagents  only.  In  the  full  cell  the  nucleus  and  a 
little  finely  granular  cytoplasm  are  forced  against  the  base  of  the 


302 


PRACTICAL  HISTOLOGY 


cell.  When  the  secretion  is  discharged  the  nucleus  moves  away  from 
the  base  and  the  cytoplasm  spreads  towards  the  distal  extremity 
of  the  cell.  In  these  tubules  of  most  of  the  mucous  and  mixed  glands 
(exceptions  are  those  of  the  soft  palate  and  base  of  the  tongue) 
other  cells_are  found  between  the  mucous  cells  and  the  basement 
membrane.  These  are  darkly  staining  cells  and  are  arranged  in  the 
form  of  crescents  and  constitute  the  crescents  of  Gianuzi,  or  demilunes 
of  Eeidenhain.  These  groups  are  chiefly  located  at  the  blind  ex- 
tremity of  the  mucous  tubules  and  although  at  times  they  may  reach 
to  the  lumen  they  are  usually  separated  therefrom  by  the  mucous 


Fig.  182. — Section  of  the  Human  Submaxillary  Gland  Showing  Mucous 

Tubules  and  Serous  Acini. 

The  lightly  stained  mucous  tubules  show  demilunes  of  Heidenhain.     (Photograph. 

Obj.  4  mm.,  oc.  7.5  X.) 

cells.  The  cytoplasm  is  quite  granular  and  the  nucleus  quite 
chromatic  and  basally  placed.  Intracellular  and  intercellular 
capillaries  are  numerous;  the  secretion  is  discharged  from  the  former 
into  the  latter  and  through  these  gains  access  to  the  lumen  of  the 
tubule.  In  this  they  resemble  true  serous  cells  and  in  addition 
Krause  has  shown  that  these  cells  will  discharge  sodium  indigo 
sulphate  granules  just  as  do  the  serous  cells.  Stohr  and  others  believe 
these  cells  to  be  the  resting  stages  of  the  mucous  cells.  The  intra- 
lobular ducts  are  unusually  large  and  distinct  in  some  animals  and 
often  represent  a  distinguishing  characteristic  of  this  gland. 

The  excretory  duct  is  the  submaxillary  duct,  or  duct  of  Wharton. 


THE  DIGESTIVE   GLANDS 


3°3 


The  sublingual  glands  really  represent  a  collection  of  glands  and 
not  an  individual  gland  upon  each  side  in  the  floor  of  the  oral  cavity. 
Each  mass  weighs  only  3  to  4  grams  and  so  represents  the  smallest 
of  the  salivary  glands.  It  is  compound  tubular  in  structure  and 
nearest  to  the  pure  mucous  glands  as  it  does  not  contain  many  serous 


Fig.  183. — Section  of  Submaxillary  Gland  of  a  Fox. 

a.  Connective  tissue;  b,  serous  acinus;  c,  intralobular  ducts;  d,  lumen  of  a  mucous 

acinus;  e,  mucous  cells;/,  demilune  of  Heidenhain;  g,  capillary. 


acini;  the  serous  portion  is  represented  by  the  crescents  of  Gianuzi. 
Occasionally  sections  of  serous  acini  are  apparently  seen  but  these 
are  said  to  represent  cross-sections  of  the  tubules,  near  the  blind  end, 
in  which  the  crescents  abound. 

There  are  usually  several  ducts,  called  the  sublingual  ducts  or 
ducts  of  Rivinus.  If  but  one  is  present  it  is  called  the  duct  of  Bar- 
tholin. 


304 


PRACTICAL  HISTOLOGY 


The  blood-vessels  of  the  pancreas  pass  into  the  interlobular  con- 
nective tissue  and  accompany  the  ducts,  to  which  they  give  branches. 
At  the  lobules  small  arterioles  center  and  form  a  capillary  plexus 
around  the  acini.  Special  arterioles  pass  to  the  islands  and  form  a 
glomerular  mass  of  capillaries  that  resembles  those  of  the  kidney. 
The  extent  will  depend  upon  the  size  of  the  island  and  these  vessels 
are  characteristic  of  the  pancreas.  The  blood  is  collected  in  venous 
channels  and  this  venous  blood  no  doubt  contains  the  harmones 


Fig.  184. — A  Portion*  of  the  Submaxillary  Gland  of  a  Rabbit. 

a,  A  cell  filled  with  secretory  granules,  b,  later  stage  of  secretory  activity  with 
the  granules  swollen;  cells  are  clear  and  show  a  reticulum;  c,  c,  secretory 
canaliculi.      {After  E.  Midler.) 


elaborated  by  the  islands;  these  are  carried  to  the  liver  by  the  portal 
vein.  By  this  vessel  the  harmones  are  delivered  to  the  liver  cells 
and  here  assist  or  cause  the  liver  cells  to  store  the  excess  sugar  and 
to  dole  it  out  in  only  the  required  amounts. 

The  lymphatics  are  numerous  in  the  interlobular  connective  tissue 
where  perivascular  plexuses  are  formed.  These  drain  the  lymph 
spaces  of  the  lobules. 

The  nerves  are  of  the  sympathetic  system  and  accompany  the 
vessels  in  the  interlobular  tissue  where  small  ganglia  may  be  numer- 


THE   DIGESTIVE   GLANDS  36$ 

ous.     Branches  supply  the  muscle  of  the  vessels  and  ducts  and  others 

pass  into  the  lobules  and  form  a  meshwork  around  the  acini  and 
pass  between  the  epithelial  cells.     In  the  pancreas  of  the  cat  Pacinian 

bodies  are  very  numerous. 

The  blood-vessels  of  the  parotid,  submaxillary  and  sublingual  glands 
are  very  numerous  and  pass  into  the  glands  in  the  same  manner. 
Within  the  lobules  a  rich  capillary  plexus  is  formed  around  the 
acini  and  the  endothelium  of  the  capillaries  may  be  in  contact 
with  the  basement  membrane  in  many  places.  The  venous  blood 
is  returned  in  a  corresponding  manner. 

The  lymphatics  are  not  so  numerous  as  in  the  pancreas  but  are 
somewhat  similar. 

The  nerves  for  the  oral  salivary  glands  are  from  both  the  cerebral 
and  sympathetic  nerve  systems.  These  nerves  pass  into  the  inter- 
lobular connective  tissue  with  the  blood-vessels.  In  the  lobules 
these  fibers  form  plexuses  around  the  walls  of  the  acini,  penetrate 
the  basement  membrane  and  terminate  in  fibrils  or  enlargements 
upon  the  epithelial  cells.  These  secretor  fibers  are  supposed  to  be 
derived  from  the  cerebral  nerves  through  the  sympathetic.  The 
fibers  to  the  blood-vessels  are  vasoconstrictor  and  vasodilator  fibers; 
the  former  are  supposed  to  come  from  the  cerebral  nerves  through  the 
sympathetics  and  the  latter  directly  from  the  sympathetics. 


20 


CHAPTER  XI 
RESPIRATORY  SYSTEM 

This  system  comprises  the  nares,  nasal  fossae,  upper  part  of  the 
pharynx,  the  larynx,  trachea,  bronchi,  lungs  and  pleurae.  Although 
there  is  no  direct  connection,  the  thyreoid  and  parathyreoids  are 
included  in  this  Chapter. 

The  nares  are  the  two  openings  that  lead  into  the  nasal  cavities. 
Here  the  skin  of  the  nose  changes  to  a  mucous  membrane  and  this 
area  constitutes  a  mucocutaneous  junction.  Just  within  each  of  the 
nares  is  the  vestibule,  or  first  part  of  the  nasal  cavity;  the  lower 
part  of  this  is  the  respiratory  part  and  the  upper  the  olfactory  portion; 
the  latter  will  be  considered  in  another  section. 

The  vestibule  is  lined  by  a  mucous  membrane  that  consists  of 
epithelial  cells,  basement  membrane  and  tunica  propria.  The  epithe- 
lial cells  are  of  the  stratified  squamous  variety  that  show  a  change 
from  the  keratinized  epithelium  of  the  skin  to  the  more  delicate  type 
as  found  in  the  internal  parts  of  the  body.  They  resemble  somewhat 
those  of  the  lip  at  the  mucocutaneous  junction  but  are  not  quite 
as  well  developed.  Near  the  outlet  there  are  some  very  large 
hairs,  the  vibrissa  that  possess  no  arrector  muscles.  These  cells 
rest  upon  a  thin  basement  membrane  and  this  is  supported  by  the 
tunica  propria  which  is  attached  to  the  cartilages  beneath.  In  this 
areolar  tissue  are  found  the  roots  of  the  hairs  and  connected  sebace- 
ous glands,  some  sweat  glands,  diffuse  lymphoid  tissue  and  at  times 
a  few  small  mucous  and  serous  glands. 

The  mucous  membrane  of  the  vestibule  continues  as  the  mucosa 
of  the  nasal  cavity  of  each  side,  and  at  the  dorsal  limit  of  the  cavities 
becomes  continuous  with  the  mucosa  of  the  nasopharynx. 

The  nasal  mucosa  likewise  consists  of  three  layers.  The  epithelium 
is,  however,  of  the  stratified  ciliated  or  pseudociliated  variety  con- 
taining goblet  cells  in  great  numbers.     Beneath  these  are  the  base- 

306 


RESPIRATORY   SYSTEM  307 

ment  membranes  (which  responds  to  the  elastica  stains)  and  tunica 
propria.  The  latter  varies  in  thickness  in  the  different  parts.  Over 
the  conchal  bones  it  is  thickest  and  in  the  accessory  sinuses  thinnest. 
It  consists  of  fibro-elastic  tissue  containing  the  vessels  and  nerves 
and  a  considerable  quantity  of  diffuse  lymphoid  tissue  and  even 
solitary  nodules.  Mucous  and  serous  glands  are  also  numerous. 
Some  smooth  muscle  tissue  is  present  and  this  chiefly  surrounds  the 
venous  channels  in  circular  or  longitudinal  bands.  The  blood- 
vessels are  very  numerous  and  in  the  thicker  parts  of  the  mucosa 
may  constitute  erectile  tissue.  The  tunica  propria  is  attached  to  the 
periosteum  of  the  bony  boundaries  of  the  nasal  cavities. 

The  accessory  cavities,  the  frontal,  ethmoidal,  sphenoidal  and 
maxillary  sinues,  are  lined  with  an  extension  of  the  mucosa  from  the 
nasal  cavities  proper.  The  mucosa  is  very  thin,  seldom  over  0.02 
mm.  and  is  firmly  attached  to  the  periosteum  of  the  bony  boundaries. 
Glands  are  not  numerous  in  these  cavities. 

The  nasopharynx  has  a  mucosa  that  is  partially  attached  to  the 
bony  wall  and  partly  attached  to  the  fibrous  and  muscle  coats  that 
extend  throughout  the  pharynx.  The  mucosa  consists  of  stratified 
ciliated  cells  that  rest  upon  a  basement  membrane  beneath  which 
there  is  a  tunica  propria  consisting  of  areolar  tissue.  Goblet  cells 
are  numerous  in  the  epithelial  layer.  Some  small  glands  and  diffuse 
lymphoid  tissue  are  found  in  the  tunica  propria,  as  well  as  solitary 
nodules;  the  latter  are  especially  numerous  in  the  dorsal  wall.  When 
these  hypertrophy  in  the  child  they  constitute  adenoids.  This 
lymphoid  tissue  constitutes  the  pharyngeal  tonsil.  The  mucosa  is 
firmly  attached  to  the  bony  dorsal  boundary  but  laterally  and 
ventrally  it  is  loosely  attached  to  the  muscles  of  the  palate  and 
tongue.  At  the  sides  of  the  nasopharynx  the  epithelial  cells  are 
continuous  with  those  lining  the  auditory  tube.  The  tunica  pro- 
pria of  the  pharyngeal  extremity  of  this  tube  contains  a  considerable 
amount  of  lymphoid  tissue  that  is  referred  to  as  the  tubal  tonsil. 

LARYNX 

The  larynx  is  a  hollow,  cartilaginous  organ  connecting  the  pharynx 
with  the  trachea.  It  consists  of  epiglottis,  vocal  cords  and  larynx 
proper. 


308  PRACTICAL  HISTOLOGY 

The  epiglottis  is  a  projecting  flap  that  protects  the  glottis  during 
deglutition.  It  is  covered  by  stratified  squamous  cells  upon  both 
sides,  and  these  are  continuous  at  the  edges,  and  rest  upon  basement 
membrane  and  pap  Mated  tunica  propria.  The  latter  is  composed 
of  fibro-elastic  tissue,  and  contains  diffuse  lymphoid  tissue,  and, 
also,  some  glands,  near  its  attachment.  In  the  epithelial  portion 
of  the  ventral  surface,  taste-buds  are  found.  Beneath  the  tunica 
propria  is  the  submucosa,  which  consists  of  loose  white  fibrous 
connective  tissue.  In  it  is  found  a  plate  of  elastic  cartilage  that 
gives  the  stiffness,  and  also  the  elasticity,  to  this  organ. 

The  vocal  cords  comprise  the  true  and  the  false.  The  former  are 
the  functionating  structures,  while  the  latter  (plica  ventrical  ares) 
are  merely  heavy  folds  of  mucous  membrane  that  seem  to  resemble 
the  former.  Mucous  glands  are  said  to  be  present  in  the  plicae. 
The  true  cords  alone  are  of  importance. 

The  true  vocal  cords,  plicae  vocales,  are  covered  by  stratified 
squamous  cells  that  are  supported  by  basement  membrane  and  tunica 
propria.  The  central  portion  consists  of  a  band  of  elastic  tissue  that 
extends  from  the  angle  of  the  thyreoid  cartilage  to  the  vocal  process 
of  the  arytenoid  cartilage.  The  epithelial  layer  is  usually  thin  and 
exposes  the  yellow  color  of  the  elastic  tissue.  A  small  nodule  of 
elastic  cartilage  (Luschka's)  is  found  in  the  ventroinferior  part  of 
each  fold.     They  contain  no  glands. 

Between  the  two  sets  of  cords  there  is  a  space,  or  recess,  on  each 
side,  called  the  ventricle  of  the  larynx.  This  is  lined  with  stratified 
squamous  cells  and  diffuse  lymphoid  tissue  is  found  in  the  tunica 
propria.  The  saccule  is  an  offshoot  of  the  ventricle  and  has  60  to  70 
small  mucous  glands  within  its  tunica  propria  which  form  a  secretion 
that  is  squeezed  out  upon  the  vocal  cords  to  lubricate  them. 

The  remainder  of  the  larynx  consists  of  mucous,  submucous  and 
fibrous  coats. 

The  mucous  coat,  including  that  of  the  ventricles,  is  lined  by 
stratified  ciliated  epithelial  cells.  The  tunica  propria  contains  a 
great  deal  of  diffuse  lymphoid  tissue.  That  portion  of  the 
submucosa  adjacent  to  the  tunica  propria  possesses  a  number  of 
small  mucous  glands.  In  its  peripheral  portion,  the  cartilage  masses 
are  found. 


RESPIRATORY   SYSTEM  309 

The  form  of  the  larynx  is  given  by  the  cartilages,  which  are  chiefly 
hyalin.  Those  of  Wrisberg  and  Santorini,  middle  of  the  thyreoid  and 
the  apices  of  the  arytenoids  are  elastic  cartilage. 

External  to  the  cartilage  is  the  fibrous  coat,  which  is  composed  of 
white  fibrous  tissue,  supports  the  other  coats,  and  connects  the 
larynx  to  the  surrounding  organs  or  tissues. 

The  arteries  are  derived  from  several  sources.  The  larger  vessels 
pass  to  the  submucous  coat  from  which  the  smaller  vessels  are  sent 
to  the  muscle  and  mucous  coats.  In  the  mucosa  the  capillaries  form 
quite  a  plexus  beneath  the  epithelium  and  around  the  glands.  The 
blood  is  collected  by  venous  channels  that  ultimately  join  the  various 
thyreoid  veins. 

The  lymphatics  are  numerous.  They  start  in  the  mucous  coat 
and  the  upper  set  passes  through  the  thyreohyoid  membrane  and 
the  efferents  conducts  the  lymph  to  the  nodes  near  the  bifurcation 
of  the  common  carotid  artery.  The  efferents  of  the  lower  set  pass 
through  the  cricothyreoid  membrane  and  conduct  the  lymph  usually 
to  the  inferior  laryngeal  node. 

The  nerves  are  from  the  vagal  and  sympathetic  nerves.  The 
cricothyreoid  and  part  of  the  arytenoid  muscles  and  the  mucosa 
are  supplied  by  the  superior  laryngeal  nerve,  while  the  remaining 
muscles  are  supplied  by  the  inferior  laryngeal  nerves.  These  ter- 
minate in  regular  motor  end-plates.  The  sympathetic  nerves  are 
for  the  muscles  and  glands.  Sensor  fibers  pass  to  the  mucosa  where 
they  terminate  between  the  epithelial  cells  in  a  network  of  fine 
fibrils.     Taste-buds  are  found  on  the  ventral  surface  of  the  epiglottis. 

TRACHEA 

The  trachea  connects  the  larynx  wTith  the  lungs,  its  lower  end 
bifurcating  to  form  the  bronchi.  It  has  three  coats,  mucous,  sub- 
mucous and  fibrous. 

The  mucous  coat  is  a  continuation  of  that  of  the  larynx.  It  is 
composed  chiefly  of  stratified  ciliated  and  goblet  cells  that  rest  upon 
the  basement  membrane  and  tunica  propria.  The  basement  membrane 
is  usually  quite  prominent,  and  the  tunica  propria  contains  consider- 
able diffuse  lymphoid  tissue.     It  consists  of  fibro-elastic  tissue,  in 


3io 


PRACTICAL  HISTOLOGY 


which  the  fibers  have  chiefly  a  longitudinal  direction.  That  portion 
of  the  mucosa  opposite  to  the  attachment  to  the  esophagus  is  lined, 
at  times,  by  stratified  squamous  cells,  and  is  usually  irregular. 

The  submucosa  is  made  up  of  white  fibrous  tissue,  and  supports 
the  large  blood-vessels  and  a  large  number  of  mucous  glands,  the 


& 


>fyv:i 


?/L 


a. 


Fig.  185; — Cross-section  of  Segment  of  the  Trachea. 

Mucous  coat;  b,  submucous  coat;  c,  d,  fibrous  coat  containing  some  vol- 
untary striated  muscle,  I,  m\  e,  stratified  ciliated  epithelium;  /,  basement 
membrane;  g,  goblet  cells;  h,  mucous  glands;  *,  blood-vessel;  k,  elastic 
tissue  and  perichondrium;  I,  longitudinal,  and  m,  cross-sections  of  voluntary- 
muscle  fibers. 


tracheal  glands.  These  lie  in  that  portion  near  the  tunica  propria 
and  the  largest  are  in  the  dorsal  part  of  the  trachea.  In  the 
peripheral  part  are  found  the  cartilage  rings. 

These  so-called  rings  are  C-shaped  masses  of  hyalin  cartilage,  with 
the  open  portion  at  the  attachment  of  the  organ  to  the  esophagus. 


RESPIRATORY   SYSTEM  31I 

These  masses  are  thickest  in  front,  and  taper  as  the  ends  are  reached. 
Although  the  cartilages  are  supposed  to  consist  of  one  piece,  they 
are  commonly  made  up  of  a  number  of  plates.  The  ends  of  the  C's 
are  connected  by  traversely  and  longitudinally  arranged  smooth 
muscle  fibers,  which  are  attached  to  the  inner  and  outer  perichon- 
driums,  and  then  bridge  the  spaces  between  the  ends  of  the  cartilage. 
This  strip  of  muscle  extends  the  length  of  the  trachea,  but  no  com- 
plete muscularis  is  present.  The  rings  are  sixteen  to  eighteen  in 
number,  and  are  separated  from  one  another  by  white  fibrous  tissue. 

The  inner  transverse  fibers  are  the  more  numerous;  the  outer  fibers 
are  arranged  in  a  few  longitudinal  bundles. 

The  fibrous  coat  lies  outside  of  the  cartilage  rings,  and  consists 
of  white  fibrous  and  yellow  elastic  tissues. 

The  blood-vessels  and  lymphatics  have  their  larger  branches  in  the 
submucosa,  from  which  smaller  vessels  extend  to  the  other  coats, 
and  form  capillaries. 

The  nerves  are  chiefly  sympathetic. 

The  bronchi  have  the  same  general  structure  as  the  trachea. 
Usually  the  C-shaped  ring  of  cartilage  is  replaced  by  a  number  of 
plates. 

LUNGS 

The  lungs  resemble  compound  tubido-alveolar  glands,  the  bronchi 
corresponding  to  the  excretory  ducts. 

Each  lung  is  invested  by  a  fibrous  sheath,  covered  almost  entirely 
by  serous  membrane,  the  visceral  layer  of  the  pleura,  which  is  re- 
flected over  the  inside  of  the  pleural  cavity,  as  the  parietal  layer  of 
the  pleura.  Between  these  two  layers  is  the  so-called  pleural  cavity, 
but  as  the  lungs  fill  it  in  the  living  condition,  it  does  not  exist  as  a 
cavity.  In  it  is  found  a  small  amount  of  lymph  that  lubricates 
the  membranes. 

The  pleurae  have  the  same  structure  as  other  serous  membranes. 
Each  consists  of  endothelial  cells  and  subendothelial  connective  tissue 
that  pass  from  the  lung  over  to  the  body  wall.  Stomata  are  not 
present  and  the  subendothelial  tissue  is  firmly  attached  to  the  sub- 
serous tissue  that  corresponds  to  the  capsule  of  other  organs.  Over 
the  thoracic  wall  the  pleura  is  but  loosely  attached.     The  elastic 


312 


PRACTICAL   HISTOLOGY 


fibers  are  numerous.  The  pleura  extends  into  the  fissures  of  the 
lung,  covering  the  opposed  surfaces  and  separating  them  completely. 

The  blood-vessels  are  numerous,  forming  extensive  capillary  plex- 
uses.    Lymphatic  plexuses  are  also  extensive. 

The  nerves  are  from  the  vagal  and  sympathetic  nerves.  The 
latter  are  vasomotor  and  the  former  are  sensor.     These  sensor  fibers 


J   c 


J>  Sh 


Fig.   i 86. — Section  of  Human  Lung. 
a,  Pleura;  b,  alveolar  septum;  c,  alveus,  or  air  sac;  d,  alveolus;  e,  intralobular 
blood-vessel;  /,   interlobular  blood-vessel;   g,   interlobular   bronchial  tube; 
h.  cartilage;  i,  branch  of  pulmonary  artery;  k,  gland. 


may  terminate  in  delicate  fibrils,  in  small  bulbous  expansions  or 
there  may  be  lamellar  corpuscles  present. 

The  subserous  tissue  constitutes  practically  the  capsule  of  the  lung 
as  it  is  continuous  with  the  interlobular  tissue  of  the  organ.  It 
consists  of  a  thin  layer  of  white  fibrous  and  a  considerable  quantity  of 
yellow  elastic  tissues.     In  guinea-pigs  a  network  of  smooth  muscle 


RESPIRATORY   SYSTEM  313 

tissue  is  found  in  this  layer,  while  in  the  lion  and  leopard  this  layer  is 
a  strong  elastic  membrane. 

Upon  the  medial  surface  of  each  lung  there  is  an  area  of  consider- 
able extent  where  the  vessels  and  ducts  enter  or  leave  the  organ. 
This  is  limited  by  the  reflection  of  the  pleura  and  is  the  hilus,  or  root. 

The  lungs,  like  other  glands,  are  merely  systems  of  tubules  that 
branch  and  rebranch,  and  are  lined  by  different  varieties  of  cells. 
Each  is  an  alveolo-tubular  gland,  and  although  no  liquid  secretion 
or  excretion  is  formed,  it  plays  an  important  part  in  the  excretion 
of  gases  and  organic  matter  from  the  blood  and  in  the  oxygenation 
of  the  blood. 

The  bronchi  divide  like  the  ducts  of  any  gland,  and,  ultimately, 
the  small  divisions  called  bronchioles  are  reached.  Each  bronchiole 
forms  a  system  separate  and  closed  from  its  neighbors.  The  bron- 
chiole (0.5  mm.  in  diameter)  divides  into  the  respiratory  bronchioles 
(0.3  to  0.4  mm.  in  diameter);  these,  in  turn,  give  rise  to  alveolar 
ducts  (0.2  mm.),  which  end  as  large  spaces,  the  alvei,  alveolar  sacs 
or  air  sacs  (0.3  by  5  mm.);  along  the  walls  of  these  divisions,  are 
found  small  depressions  the  alveoli,  or  saccules  (0.05  to  0.1  mm.), 
and  these  are  the  final  divisions. 

A  lobule  or  structural  unit,  consists  of  the  divisions  of  a  bronchiole, 
and  varies  from  0.3  cm.  to  3  cm.  in  diameter.  It  is  surrounded  by 
white  fibrous  tissue  containing  larger  vessels  and  ducts,  which  are 
called  interlobular,  are  over  0.5  mm.  in  diameter,  and  contain  carti- 
lage. The  alvei,  or  air  sacs,  are  separated  from  one  another  by  yellow 
elastic  tissue,  in  which  a  dense  capillary  plexus  is  found.  In  some 
animals  the  lobules  are  more  distinctly  outlined  by  the  abundant 
interlobular  connective  tissue.  The  ultimate  lobule  is  one  alveolar 
sac,  or  infundibulum,  with  its  six  to  eight  alveoli.  These  are  grouped 
together  to  form  secondary  lobules  and  several  of  these  form  a  large 
division.  All  are  bound  together  and  separated  from  one  another 
by  connective  tissue  that  supports  the  vessels  and  nerves.  These 
lobules  are  roughly  pyramidal  in  shape  with  the  bases  toward  the 
surface  of  the  lung  and  the  apices  toward  the  root. 

As  the  bronchus  divides  and  redivides,  the  tubules  contain  less 
and-  less  cartilage.  The  first  important  change  is  the  formation 
of  a  complete  investment  of  cartilage,  composed  of  a  number  of 


3i4 


PRACTICAL  HISTOLOGY 


plates.  As  this  occurs,  the  muscle  tissue  begins  to  increase,  so  that 
soon  a  distinct  layer  is  seen  internal  to  the  cartilage.  The  lining 
cells  are  stratified  ciliated,  but  the  whole  mucosa  becomes  irregular 
and  corrugated,  due  to  the  formation  of  longitudinal  folds;  as  the 
divisions  become  smaller,  the  cartilage  diminishes.  The  glands  dis- 
appear when  a  diameter  of  i  mm.  is  reached.  The  cartilage  is 
retained  until  a  diameter  of  0.5  mm.  is  attained. 


Fig.  187. — Reticulum  of  the  Alveoli  of  the  Lung.     {After  Mall.) 


Such  a  tubule  is  a  bronchiole  and  it  constitutes  the  apex  of  a 
secondary  lobule.  It  is  lined  by  simple  ciliated  epithelial  and  goblet 
cells,  supported  by  a  basement  membrane  and  an  elastic  tunica 
propria.  External  to  this,  the  circular  muscle  fibers  are  quite  promi- 
nent, and  as  a  result,  folds  of  the  mucosa  are  formed.  The  external 
fibrous  tissue  contains  elastic  fibers,  as  well  as  vessels  and  nerves. 
This  blends  with  the  interlobular  tissue. 

The  respiratory  bronchioles  arise  by  a  division  of  the  above 
tubules.     They  are  short  and  are  lined  partially  by  simple  ciliated 


RESPIRATORY   SYSTEM 


315 


and  partially  by  nonciliated  cells.  The  former  are  of  the  simple 
variety,  and  few  in  number.  The  nonciliated  cells  at  first  are 
columnar ,  but  quickly  give  way  to  low  cuboidal  and  flattened  cells. 
The  last  named  are  called  respiratory  epithelium.  Along  the  walls 
of  the  tubules,  little  depressions,  the  alveoli,  are  seen,  and  here  the 
respiratory  epithelium  is  marked.  Muscle  fibers  are  found  beyond 
the  tunica  propria,  and  elastic  tissue  becomes  more  abundant. 


Fig.  188. — Scheme  of  the  Termination  of  a  Bronchial  Tube. 

B,  Bronchiole;   V,  vestibule;  At,  atrium;  S,  air-sac;  C,  C,    Alveoli;  A,  lobular 

arteriole;  LV,  lobular  venule.     (After  W.  S.  Miller.) 

The  alveolar  ducts  or  infundibula  contain  many  alveoli  fined  by 
respiratory  epithelium,  which  consists  of  thin,  nonnucleated  plates 
of  various  sizes,  arranged  individually  or  in  groups.  The  smaller 
cells  are  derived  from  the  cuboidal  cells  and  are  flattened  by  in- 
spiration, and  the  larger  are  formed  by  a  fusion  of  the  smaller  ones. 
The  walls  of  these  ducts  consist  of  tunica  propria,  muscle  tissue 
and  considerable  elastic  tissue  circularly  arranged.  The  smooth 
muscle  is  in  scattered  bundles  but  at  the  end  of  the  duct  forms  a 
ring. 


3i6 


PRACTICAL   HISTOLOGY 


The  alveolar  duct  leads  into  the  alveus,  air  sac,  or  alveolar  sac. 
On  the  walls  of  this  part  are  the  small  depressions,  the  alveoli  or 
saccules.  These  are  separated  from  one  another  by  minute  parti- 
tions, or  septa,  that  consist  of  elastic  tissue  covered  by  simple  squa- 
mous cells,  the  respiratory  epithelium.  The  alveoli  of  a  system  are 
said  to  communicate  with  one  another  by  means  of  small  channels. 

or  pores,  but  Miller  states  that  these 
are  not  present  in  the  cat.  At  the 
base  of  the  alveolus,  the  elastic  tissue  is 
formed  into  a  thick  ring.  In  the  mesh- 
^^-jr  %/4M  work   of  the  elastica  of  an  alveolus  is 

found  a  dense  plexus  of  blood-capil- 
laries. The  amount  of  elastica  allows 
a  great  increase  in  size  of  the  air  sacs 
(2  or  3  times). 

The  alveoli  vary  in  size  in  the  differ- 
ent    animals;     in    adult    man,    under 
moderate  distension  they  measure  about 
0.25  mm.  but  vary  up  to  0.1  to  0.4  mm. 
A'M  In   the   cat   and  dog  they   are   visible 

/I    r      ^^Bfck  v>  upon  the  surface  of  the  lung.      They 

are  larger  at  the  surface  of  the  lung 
than  deeper  in.  In  the  infant  the 
measure  usually  under  0.12  mm.  and 
increase  from  that  on  to  old  age. 
They  are  larger  in  the  male  than  in  the 
female.  Each  lung  is  said  to  contain 
from  300  million  to  400  million  alveoli 
in  the  adult  condition. 

From  W.  S.  Miller's  careful  studies 
of  the  structure  of  the  lungs,  the  terminal  bronchioles  terminate  as 
follows:  Each  respiratory  bronchiole  divides  into  one  or  more  alveolar 
ducts,  which  widen  at  their  outer  ends.  Each  duct  opens  into 
several  atria,  which,  in  turn,  communicate  with  the  air  sacs,  or 
alvei,  on  the  walls  of  which  are  the  alveoli. 

The  circulatory  system  is  peculiar.     As  in  the  liver,  two  sets  of 
vessels  enter,  the  pulmonary  and  bronchial,  but,  unlike  those  of  the 


Fig.  189. — Cast  of  a  Single 
Air-sac  of  a  Dog's  Lung. 

A,  Atrium;  V,  vestibule;  5, 
air-sac;  P,  neck  of  air- 
sac  cut  away.  The  smaller 
projections  are  the  alveoli. 
(After  W.  S.  Miller.) 


RESPIRATORY   SYSTEM 


317 


liver,  they  do  not  unite  to  form  a  single  system,  but  remain  individual. 
There  is  some  anastomosis  between  the  two  systems  of  vessels. 

The  pulmonary  artery  conveys  the  blood  to  be  oxygenated  and  is 
the  nutrient  vessel  of  the  functionating  epithelial  cells.  It  branches 
at  the  root,  and  the  divisions  follow  those  of  the  bronchus  very 
closely,  one  for  each  division.  Between  the  lobules,  its  branches 
are  the  interlobular  divisions,  and  these  penetrate  the  lobules 
and  one  branch  accompanies  each  division  of  the  terminal  bronchiole. 
These  form  the  densest  capillary  plexus  of  the  body,  within  the  elastica. 


Fig.   190. — Section  of  an  Injected  Lung  of  a  Dog.. 
(Photograph.     Obj.  16  mm.,  oc.  7.5  X-) 


of  the  alveoli.  Here  the  endothelial  cells  of  the  capillary,  and  the 
squamous  epithelial  cell  of  the  alveolus,  separate  the  blood  from  the 
air.  Such  an  exceedingly  thin  membrane  allows  the  interchange 
of  oxygen  and  effete  gases,  and  also  the  absorption  of  nutrient  matter 
by  the  epithelial  cells,  and  the  outward  passage  of  the  waste  matter.. 
At  the  periphery  of  each  lobule  the  blood  is  collected  by  the  venous: 
radicals  of  the  pulmonary  vein,  and  these  unite  to  form  the  inter- 
lobular branches,  that  ultimately  form  the  pulmonary  veins.     These 


318  PRACTICAL  HISTOLOGY 

interlobular  veins  run  an  independent  course  and  are  not  so  close  to 
the  smaller  bronchial  tubes  as  the  arterial  branches  are. 

The  bronchial  artery  branches  somewhat  as  the  pulmonary 
artery,  but  its  divisions  do  not  penetrate  to  the  same  degree.  The 
branches  of  the  bronchial  artery  lie  in  the  walls  of  the  bronchial 
tubes  and  nourish  them,  but  not  the  respiratory  epithelium-.  Between 
these  two  sets  of  vessels,  the  pulmonary  and  bronchial  arteries, 
there  is  some  anastomosis,  so  that  the  pulmonary  veins  carry  some 
of  the  bronchial  artery  blood  from  the  lungs.  The  bulk  of  the 
bronchial  blood,  however,  is  collected  by  the  divisions  of  the  bron- 
chial veins  that  finally  empty  into  the  vena  azygos,  right  and  left 
(or  left  superior  intercostal). 

From  this  it  is  readily  seen  that  the  bronchial  arteries  supply  only 
the  larger  bronchial  tubes.  All  of  the  smaller  ones  (those  within 
the  lobules),  the  alveolar  ducts,  alveoli,  intralobular  tissue  and  the 
pleura  are  supplied  or  nourished  by  the  pulmonary  artery. 

The  lymphatics  accompany  the  veins  and  comprise  a  superficial 
and  a  deep  set.  The  former  lies  under  the  pleura  and  its  efferents 
pass  the  lymph  into  the  deep  set.  These  deeper  lymphatics  start 
in  the  lobules  in  the  intercellular  spaces;  the  vessels  lie  in  the 
interlobular  tissue  and  accompany  the  veins.  The  bronchial  tubes 
of  large  size  may  have  a  plexus  of  lymph  vessels  in  the  mucous  coat 
and  another  in  the  submucous  coat  peripheral  to  the  cartilage. 
These  communicate  with  those  around  the  pulmonary  artery  and 
vein  branches.  In  the  interlobular  connective  tissue  there  may  be 
considerable  diffuse  lymphoid  tissue  and  solitary  nodules;  lymph 
nodes  may  be  found  at  the  bifurcation  of  the  bronchial  tubes. 
These  usually  contain  numerous  dark  granules  that  represent 
inhaled  dust  particles.  These  are  conveyed  to  the  lymphoid  struc- 
tures by  the  leukocytes  that  have  a  phagocytic  action. 

The  nerves  are  derived  from  the  pulmonary  plexuses  that  contain 
both  sympathetic  and  vagal  fibers.  The  motor  fibers  are  for  the 
muscle  tissue  of  the  bronchial  tubes  and  the  blood-vessels  and  the 
sensor  fibers  are  for  the  mucosa  of  the  bronchial  tubes  and  the 
epithelium  of  the  alveoli. 

The  following  are  the  epithelial  cells  that  line  the  various  portions 
of  the  respiratory  tract: 


Larynx 


RESPIRATORY   SYSTEM  319 

(  First  tart Stratified  squamous. 

I  Second  pas  i    Stratified  ciliated. 

Pharynx Stratified  ciliated. 

Epiglottis Stratified  squamous. 

Vocal  cords Stratified  squamous. 

Remainder  of 

.Larynx Stratified  ciliated. 

Trachea Stratified  ciliated. 

Bronchi Stratified  ciliated. 

Bronchial  Tubes Stratified  ciliated. 

Simple  ciliated. 

Bronchioles Simple  columnar. 

Simple  squamous  (respiratory). 

Alveolar  Ducts Simple  squamous  (respiratory) 

Alveoli Simple  squamous  (respiratory). 

THYREOID  BODY 

The  thyreoid  body  is  a  ductless,  compound  tubular  gland,  and  con- 
sists of  two  large  lateral  lobes  united  by  a  narrow  band,  the  middle 
lobe,  or  isthmus. 

The  organ  is  surrounded  by  a  capsule  of  dense  white  fibrous 
tissue  that  sends  in  septa,  which  divide  the  gland  into  lobes  and 
lobules.  These  divisions  are  irregular,  and  the  lobules  are  composed 
of  a  number  of  short  tubules,  or  vesicles,  sometimes  called  follicles, 
that  vary  considerably  in  diameter.  Each  tubule  is  oval  or  round 
in  shape  and  is  lined  by  cuboidal  epithelial  cells  that  rest  upon  a 
basement  membrane;  outside  of  this  is  the  intralobular,  or  intertubular , 
connective  tissue  that  supports  the  blood-vessels.  The  cells  are 
said  to  be  of  two  kinds:  (1)  Chief  cells;  (2)  colloid  cells.  The  first 
are  said  to  become  the  second  and  these  in  turn  change  into  the 
colloid  substance.  The  cytoplasm  contains  granules  that  are  acid- 
ophilic in  reaction.  Fat  droplets  and  granules  that  give  the  colloid 
reaction  are  also  found.  Intercellular  capillaries  are  said  to  exist 
between  the  cells.  In  the  tubules  is  seen  a  peculiar,  homogeneous 
substance,  the  colloid  substance,  that  is  supposedly  the  result  of  the 
activity  of  the  cells.  If  a  fresh  organ  be  cut  a  glairy  substance 
oozes  out.  It  has  a  yellowish  color,  and  as  blood-cells  are  frequently 
seen  in  it,  the  color  may  be  due  to  the  hemoglobin  from  these. 
It  contains  iodin  in  the  form  of  iodothyrin.     Sometimes,  the  colloidal 


320  PRACTICAL   HISTOLOGY 

material  is  shrunken,  and  then  its  edges  are  crenated;  in  such 
tubules,  the  epithelial  cells  are  drawn  away  from  the  basement 
membrane.  Gulland  and  Goodall  found  granules  of  iron  in  the 
interlobular  tissue  cells  and  in  the  epithelial  cells  of  the  tubules. 
These  granules  were  most  abundant  in  those  tubules  in  which  the 
colloid  substance  was  small  in  amount.  The  colloid  material  and 
cells  vary  in  appearance  in  different  individuals;  this  difference  may 
depend  upon  diet  and  nutritional  conditions. 


rt*fcg^ 


/         i*  •  Mi  ^r,  %i*    . 


.•    .. 


-.-. 


.  ■  •»•■ 


K  *£ 


-.. 


- 


Fig.  191. — Section  of  Human  Thyreoid  Gland. 

a.    Epithelium;   b,    basement   membrane;   c,    colloid   substance;   d,   interlobular 
connective  tissue;  e,  interlobular  vein. 

It  is  not  unusually  found  that  the  colloid  substance  in  the  same 
tubule  is  of  different  reaction,  most  of  its  responding  to  plasmatic 
stains,  while  a  smaller  amount,  centrally  located  and  surrounded 
by  the  preceding,  responds  to  the  nuclear  stain. 

Blood-vessels  are  numerous,  and  dense  plexuses  are  formed  around 
the  tubules.  It  is  thought  that  the  colloid  material  may  represent 
an  internal  secretion  that  is  absorbed  by  the  blood-vessels,  or  per- 
haps the  lymphatics. 

The  lymphatics  are  numerous,  and  lie  between  the  tubules.  They 
often  contain  some  of  the  colloid  substance. 


RESPIRATORY   SYSTEM 


321 


The  nerves  are  derived  from  the  sympathetic  system.  They  form 
fine  plexuses  in  the  walls  of  the  tubules;  from  this  terminal  fibrils 
end  upon  and  between  the  epithelial  cells.  Other  branches  pass 
to  the  muscle  tissue  of  the  vessels. 


PARATHYREOIDS 

The  parathyreoids  are  usually  four  in  number,  two  of  which  lie 
in  close  relation  with  each  lateral  lobe  of  the  thyreoid.  They  are 
small,  and  the  epithelial  cells  are  usually  of  the  glandular  type,  and 
are  arranged  in  groups,  or  chains,  forming  a  network,  or  even  tubules. 


Fig.  192. — Section  of  Human  Parathyreoid  Gland. 
Some  of  the  spaces  show  colloid  substance.     (Photograph.     Obj.  32  mm.,  oc. 

5  X.) 

Each  is  surrounded  by  a  capsule  of  white  fibrous  tissue  that  is  thin 

but  tough.     Within  this  there  is  a  delicate  reticulum  that  supports 

the  epithelium,  vessels  and  nerves.     These  cells  respond  very  readily 

to  the  protoplasmic  stains  and  are  usually  quite  deeply  stained,  in 

marked  contrast  to  the  cells  of  the  thyreoid  body.     Rulison  states 

that  there  are  two  kinds  of  cells:  The  principal  cells  are  the  smaller 

and  most  numerous.     These  are  oval  in  shape,  the  cytoplasm  is 

clear  and  the  nucleus  vesicular  in  appearance.     The  acidophilic  cells 
21 


322  PRACTICAL   HISTOLOGY 

are  larger  cells  in  which  the  cytoplasm  contains  a  number  of  acido- 
philic granules.  The  nucleus  is  smaller  and  contains  much  chro- 
matin. Between  the  cells  is  white  fibrous  connective  tissue  that 
supports  quite  a  capillary  plexus.  Occasionally,  colloid  material  is 
seen  in  the  tubules.  When  the  thyreoids  are  removed  and  the 
parathyreoids  remain,  they  hypertrophy  and  carry  on  the  function 
of  the  removed  organs.  According  to  some  investigators,  the  para- 
thyreoids do  not  assume  the  function  of  the  thyreoids.  Removal  of 
the  parathyreoids  is  fatal  within  a  short  time. 


CHAPTER  XII 
THE  URINARY  SYSTEM 

The  urinary  organs  comprise  the  kidneys,  ureters,  bladder  and 
urethra.  On  account  of  its  proximity  to  the  kidney,  the  adrenal 
will  also  be  considered. 

The  kidney  is  a  compound  tabular  gland,  and,  next  to  the  liver,  the 
largest  in  the  body.  The  kidneys  represent  the  urea  excreting 
organs  while  the  ureters,  bladder  and  urethra  are  the  conducting 
tubes,  reservoir  and  outlet  tube  by  means  of  which  the  urine  is  car- 
ried, stored  and  emptied.  The  kidneys  lie  in  the  dorsal  portion 
of  the  abdominal  cavity  dorsal  to  the  peritoneum.  Each  is  sur- 
rounded by  a  considerable  quantity  of  adipose  tissue  called  the  peri- 
renal fat.  The  quantity  depends  upon  the  nutritive  condition  of  the 
body  and  in  some  animals  constitutes  an  enormous  mass  in  which  the 
kidney  appears  as  a  very  small  part.  Some  of  this  fat  persists  even 
though  the  animal  dies  of  starvation. 

The  kidney  is  surrounded  by  a  thin  capsule  of  white  fibrous 
tissue  that  normally  strips  readily  from  the  organ.  This  is  of  great 
importance,  wThen  the  organ  is  studied  pathologically.  It  consists 
of  white  fibrous  tissue  containing  some  smooth  muscle  and  elastic 
fibers.  It  continues  into  the  organ  in  the  form  of  small  trabecular 
which  form  the  gross  framework  of  the  organ;  within  this  there  is  a 
delicate  network  of  reticulum  that  supports  the  parenchyma,  vessels 
and  nerves.  At  the  hilus  the  capsular  tissue  blends  with  that  of 
the  pelvis  of  the  ureter  and  forms  a  mass  of  areolar  tissue  that  sur- 
rounds the  pelvis  and  blood-vessels  and  fills  the  renal  sinus.  Adipose 
tissue  is  deposited  in  this  tissue.  Although  the  trabecular  tend  to 
divide  the  kidney  into  lobes  and  lobules  only  parts  of  the  lobes  are 
distinct  in  the  adult  condition.  These  are  represented  by  the  apices 
of  the  medullary  pyramids,  the  bases  of  which  are  somewhat  sepa- 
rated from  one  another  by  the  columns  of  Bertin.     The  cortical 

323 


324 


PRACTICAL   HISTOLOGY 


portion  shows  no  lobulation,  but  in  the  fetal  condition  the  surface  of 
the  kidney  is  nodulated  and  these  nodules  indicate  the  lobules;  by 
birth  these  lobules  are  all  fused  and  give  the  surface  a  smooth,  even 
contour  in  most  animals.     In  reptiles,  birds  and  some  mammals 


-a 


1 

Fig.  193. — Section  of  Human  Kidney  showing  Cortex  and  Medulla. 
a.  Capsule;  b,  cortex;  c,  medulla;  d,  labyrinth;  e,  medullary  ray;/,  renal ";  bodies; 
g,  area  in  which  renal  body  has  dropped  out;  h,  capsule  of  Bowman;  i, 
glomerulus;  k,  afferent  arteriole;  /,  neck  of  uriniferous  tubule;  m,  tubules 
of  labyrinth;  n,  longitudinal  sections  of  collecting  tubules;  o,  cross-sections 
of  collecting  tubules. 

these  lobulations  are  retained  throughout  life.  In  the  guinea-pig, 
cat  and  rabbit  no  lobulation  whatever  is  noticeable.  A  renculus 
is  represented  by  a  single  medullary  ray  surrounded  by  the  adjacent 


THE   URINARY   SYSTEM  325 

convoluted  tubules  of  the  labyrinth.  The  interlobular  vessels 
constitute  its  boundary. 

Beneath  the  capsule  is  the  kidney  substance  that  comprises  the 
interstitial  tissue,  or  supportive  substance  already  mentioned,  and 
the  parenchyma,  the  functionating  part  that  consists  of  epithelium 
arranged  in  the  form  of  tubules.  These  uriniferous  tubules  are  com- 
paratively long  and  have  a  very  irregular  course.  These  consist 
of  a  single  layer  of  epithelial  cells,  basement  membrane  and  tunica 
propria.  The  homogeneous  substance  of  the  basement  membrane 
is  very  resistant  to  acids.  When  pieces  of  the  kidney  are  subjected 
to  hydrochloric  acid  the  interstitial  tissue  is  dissolved  but  the  base- 
ment membrane  remains  intact  and  holds  the  tubule  together  in 
its  entirety.  In  this  way  beautiful  mounts  of  these  tubules  may  be 
obtained.  In  special  preparations  Mall  has  shown  that  the  base- 
ment membrane  contains  delicate  fibrils  that  are  continuous  with 
the  reticulum  of  the  interstitial  tissue.  These  fibers  are  circularly 
and  longitudinally  arranged.  These  are  imbedded  in  the  homoge- 
neous substance  which  alone  shows  in  the  ordinary  preparations. 
The  tunica  propria  of  the  convoluted  tubules  is  not  prominent. 
Along  the  medial  margin  of  the  organ  is  a  deep  notch,  the  hilus,  at 
which  the  renal  artery  and  nerves  enter  and  the  renal  vein,  ureter 
and  lymphatics  leave. 

When  the  organ  is  sectioned,  upon  microscopic  examination  it 
is  seen  to  consist  of  an  outer  margin,  the  cortex,  and  an  inner  broader 
portion,  the  medulla.  Just  within  the  hilus  is  seen  a  space,  the 
sinus.  In  the  ordinary  condition  this  is  not  a  space  as  it  contains 
the  pelvis  of  the  ureter,  the  branches  of  the  renal  artery,  the  tribu- 
taries of  the  renal  vein,  nerves  and  lymphatic  trunks  imbedded  in 
adipose  tissue.  If  these  structures  be  removed  then  the  space  is 
demonstrable. 

The  cortex  constitutes  the  outer  third  of  the  organ,  and  is  further 
subdivided  into  medullary  rays  and  labyrinth.  This  division  is  rep- 
resented by  the  alternating  dark  and  light  bands,  which  are  at  right 
angles  to  the  capsule,  and  gives  a  striated  appearance  to  the  cortex. 

The  medullary  rays,  or  pyramids  of  Ferrein,  consist,  microscopic- 
ally, of  the  straight  portions  of  the  tubules  that  extend  from  the 
medulla  into  the  cortex,  surrounded  by  the  intertubular,  or  inter- 


326 


PRACTICAL   HISTOLOGY 


stitial  reticulum.  They  never  extend  to  the  capsule,  but  diminish 
in  width  as  the  outer  portion  of  the  cortex  is  approached. 

The  labyrinth  lies  between  the  medullary  rays,  and  is  composed  of 
the  Malpighian,  or  renal,  corpuscles,  the  starting  points  of  the  tubules, 
and  the  convoluted  portions  of  the  uriniferous  tubules.  These  are 
supported  by  the  interstitial  connective  tissue  that  contains  the 
blood-vessels. 

The  renal  corpuscles  are  found  only  in  the  cortex,  and  here  are 
limited  to  the  labyrinth.     There  are  probably  over  a  million  of  these 


Fig.  194. — Section  of  the  Cortex  of  the  Human  Kidney. 

a,  Labyrinth;  b,  medullary  ray.      (Photograph.       Obj.  16  mm.,  oc. 


7-5  X.) 


renal  corpuscles  in  each  human  kidney.  In  the  cat  there  are  16,000 
in  each  kidney.  Each  one  consists  of  a  tuft  of  arterial  capillaries, 
the  glomerulus,  or  renal  tuft,  surrounded  immediately  by  a  delicate 
double  membrane  of  simple  squamous  cells,  resting  upon  a  basement 
membrane.  The  inner  layer  lies  upon  the  tuft,  and  the  outer  forms 
the  wall  of  the  tubule.  This  membrane  is  Bowman's  capsule, 
and,  with  the  tuft,  comprises  the  renal  corpuscle.  The  tuft  itself 
is  not  a  simple  structure.     The  arteriole,  upon  entering,  divides 


THE   URINARY   SYSTEM  327 

into  a  number  of  branches,  each  of  which  forms  a  set  of  capillaries. 
This  apparent  lobulation  is  quite  distinct.  As  these  capillaries 
unite  to  form  an  efferent  arteriole,  this  arrangement  is  called  a  retia 
mirabilia.     The  afferent  arteriole  is  larger  than  the  efferent. 

The  medulla  is  sharply  outlined  from  the  cortex,  microscopically, 
by  the  absence  of  renal  corpuscles  and  the  regularity  of  the  tubules. 
At  the  junction  are  to  be  found  the  great  vessels,  and  this  portion  is 
called  the  boundary  zone.  The  medulla  consists  of  the  medullary, 
or  Malpighian  pyramids,  separated  from  one  another  by  the  columns 
of  Bertin. 

The  medullary  pyramids  are  ten  to  sixteen  in  number.  Their 
bases  continue  with  the  cortex,  and  their  apices  are  directed  toward 
the  hilus  and  project  into  the  sinus.  Each  consists  of  a  large  number 
of  straight  tubules  that  become  fewer  in  number  as  the  apex  is 
reached,  where  but  fifteen  to  twenty  are  present.  These  are  the 
papillary  ducts,  or  ducts  of  Bellini.  The  tubules  are  supported  by 
reticulum,  in  which  the  capillaries  are  found. 

The  pyramids  are  separated  from  one  another  by  a  narrow  band 
of  tissue  that  is,  near  the  apices,  chiefly  white  fibrous;  toward  the 
bases,  the  cortical  parenchyma  begins  to  enter  into  its  formation. 
This  is  the  column  of  Bertin,  and  within  it  are  the  large  vessels  that 
pass  from  the  sinus  to  the  boundary  zone. 

The  pyramids  represent  the  embryonal  condition  when  the 
whole  organ  consisted  of  lobes.  At  birth,  usually,  the  bases  of  the 
lobes  have  fused  to  form  the  cortex,  but  the  inner  ends  never  reach 
that  condition.  The  columns  of  Bertin  then  represent  the  interlobar 
connective  tissue  and  spaces.  In  some  animals  the  lobulation  never 
disappears. 

The  uriniferous  tubule  has  a  very  peculiar  and  convoluted  course. 
It  starts  in  the  cortex,  and  passes  into  the  medulla,  to  return  to  the 
cortex  for  its  final  passage  through  the  medulla.  It  originates 
at  the  renal  corpuscle,  which  is  merely  the  invaginated  end  of  the 
tubule,  containing  a  tuft  of  capillaries.  From  this,  the  presence  of  a 
double  capsule  can  be  readily  understood. 

The  inner  layer  of  this  capsule  covers  the  tuft  of  capillaries  follow- 
ing alfof  its  irregularities;  the  only  gap  is  where  the  arterioles  make 
connection  with  the  glomerular  tuft.     The  outer  layer  is  continuous 


328 


PRACTICAL  HISTOLOGY 


with  the  inner  at  the  point  of  this  reflection  over  the  arterioles. 
The  external  surface  of  the  glomerular  layer  and  the  internal  surface 
of  the  outer  layer  are  lined  with  a  single  layer  of  squamous  epithelial 
cells  that  are  almost  in  contact  with  each  other,  the  narrow  space 
represents  the  lumen  of  the  first  part  of  the  uriniferous  tubule. 
The  outlet  of  this  space  is  opposite  to  the  point  of  connection  of 
the  blood-vessels  and  represents  the  neck  of  the  uriniferous  tubule. 
The  epithelial  cells  contain  an  oval  nucleus  and  the  cytoplasm  is 


Fig.   195. — Section  of  a  Renal  Corpuscle  of  the  Preceding  Section  under 
Higher  Magnification.     (Photograph.     Obj.  4  mm,  oc.     5  X.) 

clear.  The  layer  of  cytoplasm,  however,  is  so  thin  that  the  nucleus 
bulges.  These  cells  rest  upon  a  thin  delicate  basement  membrane 
that  is  homogeneous  and  is  supported  by  a  thin  layer  of  white 
fibrous  tissue  that  represents  the  tunica  propria  of  the  ordinary 
mucous  membrane.  This  layer  is  said  to  be  thicker  in  those  cor- 
puscles near  the  medullary  region  of  the  cortex.  The  epithelial 
cells  of  the  internal  layer  of  the  capsule  are  in  direct  contact  with  the 
endothelium  of  the  Capillaries  simulating  a  sinusoidal  condition. 
This  facilitates  the  rapid  discharge  of  water  into  the  capsule  during 
the  formation  of  the  urine. 


THE   URINARY   SYSTEM  329 

The  neck  is  one  of  the  narrowest  and  most  constricted  portions  of 
the  tubule.  It  is  short  and  rapidly  goes  over  into  the  first  convoluted 
portion.  It  is  lined  by  simple  squamous,  or  low  cuboidal  epithelial 
cells.     These  rest  upon  the  basement  membrane  and  tunica  propria. 

The  proximal  convoluted  tubule  is  the  next  division  and  is  called  the 
distal  convoluted  tubule  in  embryology.  This  part  is  very  irregular 
and  tortuous  in  its  course.  It  lies  in  the  labyrinth  and  is  the  longest 
and  widest  portion  of  the  actively  functionating  portions  of  the 
tubule.  The  two  convoluted  tubules  form  the  greatest  part  of 
the  cortex.     The  cells  are  of  the  columnar  type  but  they  are  irregular 


Fig.   196. — Portion  of  a  Longitudinal  Section  of  a  Convoluted  Tubule 

Prepared  by  the  Golgi  method.     The  irregular  lines  represent  the  outline  of  the 

cells.     {After  Landauer.) 

in  height  so  that  not  only  is  the  tubule  tortuous  but  the  lumen  itself 
is  irregular  and  tortuous.  While  the  basal  and  lumen  boundaries 
of  the  cells  are  distinct  the  lateral  boundaries  are  not  readily  seen. 
They  may  be  outlines  with  silver  nitrate  solutions.  Under  this 
condition  the  outlines  are  seen  to  be  very  irregular,  resembling  the 
sutures  of  the  skull  as  the  cells  articulate  with  one  another.  The 
cytoplasm  varies  in  appearance.  In  the  lumen  end  of  the  cell  it  is 
usually  clear  or  faintly  striated  and  presents  a  cuticular  border. 
This  does  not  always  show  as  this  portion  of  the  cell  is  easily  injured. 
Thes  basal  portion  of  the  cell  contains  the  lightly  staining  nucleus 
in  which  the  chromatin  is  rather  evenly  scattered.  The  cytoplasm 
shows  striations  or  cytoreticulum.  The  granules  are  arranged 
in  the  form  of  filaments  (probably  mitochondria)  connected  with  the 


33° 


PRACTICAL   HISTOLOGY 


formation  of  urinary  excretions.  Under  the  influence  of  diuretics 
the  granules  in  the  cells  of  the  convoluted  tubules  become  fewer, 
larger  and  scattered.  Diet  also  affects  them  and  they  are  more 
numerous  after  a  pure  meat  diet.  These  granules  are  probably 
derived  from  the  disintegrating  filaments  that  probably  represent 
mitochondria.     The  state  of  secretory  activity  of  the  cells  is  indicated 


Jtf- 


mr. 


Fig.  197. — Interstitial  Tissue  of  the  Cat's  Kidney. 

M,  M,  Spaces  occupied  by  renal  corpuscles;  mr,  spaces  occupied  by  the 
tubules  of  the  medullary  rays;  the  other  parts  represent  the  labyrinth. 
(After  Disse.) 


by  a  dome-like  swelling  of  the  lumen  area  of  the  cells;  here  a  centro- 
some  may  be  observed  and  in  some  animals  the  convoluted  tubule 
cells  may  be  ciliated.  These  probably  indicate  the  ciliated  cells  of 
the  nephridia  of  invertebrates.  In  hibernating  animals  these  cells 
are  tall  and  nearly  occlude  the  lumen,  representing  the  resting  or  in- 
active stage. 


THE   URINARY   SYSTEM  33 1 

The  descending  limb  of  Henle's  loop  is  the  continuation  of  the 
preceding  part.  It  is  one  of  the  narrowest  parts  of  the  uriniferous 
tubule  and  extends  from  the  cortex  into  the  medulla.  It  is  lined 
by  simple  squamous  epithelial  cells  in  which  the  cytoplasmic  layer 
is  thin  and  the  nuclei  bulge.  The  cytoplasm  is  finely  granular  and 
the  nucleus  stains  quite  deeply  and  bulges.  As  the  nuclei  sort  of 
alternate  their  projection  into  the  lumen  makes  the  cavity  of  this 
part  of  the  tubule  irregular.  The  cells  rest  upon  the  basement 
membrane  and  beyond  this  is  the  tunica  propria. 

The  loop  of  Henle  and  the  ascending  limb  are  the  continuations  of 
the  descending  limb.  The  position  of  the  loop  depends  upon  the 
position  of  the  renal  corpuscles;  if  these  are  near  the  capsule  of  the 
kidney  the  loops  are  near  the  cortico-medullary  boundary  zone; 
if  the  corpuscles  are  near  the  medulla  the  loops  are  deeper  in  the 
medulla.  The  loop  may  be  of  the  same  size  and  structure  as  the 
descending  limb  or  may  correspond  in  these  conditions  with  the 
ascending  limb.  The  ascending  limb  extends  from  the  medulla  into 
the  cortex,  is  double  the  diameter  of  the  descending  portion  and  is 
lined  therefore  with  cuboidal  cells  that  are  quite  regular  in  height 
and  have  distinct  outlines.  The  cytoplasm  is  usually  finely  granular 
and  basal  striations  may  be  present.     The  nucleus  stains  well. 

The  distal  convoluted  tubule  is  called  the  proximal  convoluted 
tubule  in  embryology.  This  is  smaller  in  diameter  and  shorter 
than  the  first  convoluted  tubule  but  like  it  lies  in  the  labyrinthine 
portion  of  the  cortex.  The  lumen  is  irregular  here  also  because  the 
epithelial  cells  are  of  unequal  height.  Outside  of  being  shorter 
these  cells  resemble  those  of  the  proximal  part  in  structure  and 
function. 

The  arched  connecting  tubules  and  the  remainder  of  the  uriniferous 
tubules  represent  merely  conducting  portions.  This  tubule  is 
short,  lies  in  the  cortex  and  is  the  connecting  link  between  the  last 
convoluted  and  the  first  collecting  tubules.  The  cells  are  of  the 
regular  cuboidal  type  with  distinct  outlines  and  darkly  staining 
nuclei.  The  cytoplasm  is  usually  clear  and  stains  lightly.  The  lumen 
is  regular. 

The  straight  collecting  tubules  have  a  straight  course  and  begin  in 
the   cortex,  pass  into  the  medulla,  where  many  join  together  in- 


332  PRACTICAL  HISTOLOGY 

creasing  in  size  and  terminate  in  the  papillary  ducts.  In  the  cortex 
they  form  the  medullary  rays  and  in  the  medulla  they  are  parallel 
to  one  another.  The  epithelial  cells  vary  in  form  in  the  different 
portions.  In  the  cortex  where  the  diameter  is  least  the  cells  are  of 
the  cuboidal  type;  as  the  diameter  increases  the  cells  become  gradually 
columnar  of  a  low  and  then  of  the  tall  type.  The  cytoplasm  is 
clear,  the  nucleus  stains  well  and  the  cell  outline  is  distinct. 

The  papillai y  ducts,  or  ducts  of  Bellini  represent  the  terminals  of 
the  uriniferous  tubules.  There  are  fifteen  to  eighteen  of  these  ducts 
in  each  medullary  pyramid  apex  and  these  represent  the  junctions 
of  thousands  of  the  straight  collecting  tubules.  They  are  very 
great  in  diameter  and  the  epithelial  cells  lining  them  are  of  the  very 
tall  columnar  type.  The  cytoplasm  is  clear  and  the  nucleus  stains 
deeply.  In  some  animals  these  ducts  are  lined  with  stratified  colum- 
nar cells. 

The  various  portions  of  the  uriniferous  tubule  are  distributed 
as  follows: 

Cortex. — In  the  labyrinth  are  found  the  renal  corpuscles,  neck, 
first  and  second  convoluted  tubules.  In  the  medullary  rays,  the  upper 
ends  of  the  descending  and  ascending  limbs  of  Henle's  loop  and  straight 
collecting  tubules,  and  the  arched  connecting  tubule. 

Medulla. — The  lower  ends  of  the  descending  and  ascending  limbs 
and  the  loop  of  Henle  and  the  straight  collecting  tubules  and  papillary 
ducts. 

The  diameter  of  the  different  parts  of  the  tubule  varies.  The 
renal  corpuscle  is  large,  measuring  120  to  200  microns.  The  neck 
averages  about  15  microns,  and  the  proximal  convoluted  tubule 
is  quite  irregular,  but  the  average  is  about  50  to  60  microns.  The 
descending  limb  is  quite  narrow,  10  to  13  microns,  and  the  ascending 
limb  about  25  microns.  In  the  second  convoluted  tubule,  the  diameter 
again  increases,  averaging  40  to  45  microns.  From  the  beginning 
of  the  straight  tubule  to  the  end,  the  diameter  progressively  in- 
creases 18  to  50  microns;  so  that  the  papillary  ducts  may  have  a 
diameter  of  200  to  300  microns. 

The  blood-vessels  have  a  characteristic  distribution.  The  renal 
artery  passes  through  the  hilus  and  enters  the  sinus,  where  it  divides 
into  four  or  five"  branches,  of  which  the  greater  number  supply  the 


THE   URINARY    SYSTEM 


333 


_    5 


fc~  6 


ventral  three-fourths  of  the  kidney.  The  branches  that  go  to  the 
ventral  pyramids  carry  three-fourths  of  this  blood.  The  rest  of 
the  kidney  is  supplied  by  the  dorsal  branches.  The  branch  that 
supplies  each  pole,  derived  from  the  ventral  division,  divides  into 
ventral,  middle  and  dorsal  branches,  which  are  in  no  way  united. 
The  trunks  pass  up  through  the  columns 
of  Berlin,  where  small  branches  are 
given  off  to  the  vessels  and  tissues, 
as  the  interlobar  branches.  These 
branches  pass  to  the  boundary  zone, 
where  they  arch  between  the  cortex 
and  medulla,  forming  the  arterial 
arches,  or  arcade.  From  the  cortical 
side  of  the  arch,  the  cortical,  or  interlob- 
ular, arteries  are  sent  toward  the  cap- 
sule; from  these,  small  arterioles 
afferent,  pass  to  the  renal  corpuscles, 
enter  and  form  several  smaller  branches, 
each  of  which  breaks  into  a  capillary 
tuft.  From  this,  it  will  be  seen  that 
the  renal  tuft  consists  of  several 
bunches  of  capillaries.  Each  capillary 
group  is  separate,  and  the  vessels  unite 
to  form  arterioles  that  leave  the  tuft  as 
a  single  vessel,  the  efferent  arteriole. 
The  blood  is  still  arterial.  The  efferent 
arterioles  soon  form  dense  plexuses  of 
capillaries  around  the  tubules  of  the 
labyrinth  and  medullary  rays.  Those 
capillaries  near  the  boundary  zone  pass 
into  the  medulla  and  surround  the 
tubules  there.  The  capillaries  become 
venous  in  character,  and  unite  with  others  to  form  the  interlobular 
veins.  The  cortical  artery  continues  to  the  capsule,  where  it  forms 
a  star-shaped  mass  of  venules,  the  venae  stellatae.  These  are,  in 
reality,  the  starting-points  of  the  interlobular  veins,  which  run 
parallel  to  the  arteries  of  the  same  name,  and  empty  into  a  venous 


Fig.  198. — Section  of  In- 
jected Kidney  of  Guinea- 
pig. 

1 ,  I  n  t  e  r  l_o  b  u  1  a  r  (cortical) 
artery;  2,  afferent  vessel; 
3,  efferent  vessel;  4,  capil- 
lary network  in  medullary 
ray;  5,  capillary  network  in 
labyrinth;'  6,  interlobular 
(cortical)  vein.  (Stohr's 
Histology.) 


334 


PRACTICAL  HISTOLOGY 


Lobule 


Lobule 


Arched  collect- 
ing tubule 

Distal  convo- 
luted tubule 


Proximal  con- 
voluted tubule 


Capsule 


Distal  convo- 
luted tubule 

Ascending 
limb 


Descending 
limb 


Collecting 
tubule 


'Tunica  fibrosa 


•Stellate  vein 


:-i\-  .■   y  .      '.j .■/■;;;-  />•>£     tT  art 

L    >Ti^ /i;  ,.|  *r-^H$- -Int 

-1$1  "'-,'."'.■.  §$#11 yfi^M        vei 


■    "J 


Papillary  duct 


■    —•"-!  1   - 

*■.     ^.',-:     .    . 

•  '    *V'rJ    : 

I     :;  !"^/  ■."..+ 

terlobular 
artery 

terlobular 
ein 


Arciform 
artery 

Arciform  vein 


Interlobular 
artery 

Interlobular 
vein 


Fig.  199.—  Diagram  of  the  Course  of  the  Renal  Blood  Vessels. 

{Lewis  and  Stohr.) 


THE    URINARY   SYSTEM  335 

arcade  that  is  formed  at  the  boundary  zone  by  the  union  of  the 
large  vessels.     Such  is  the  blood  supply  of  the  cortex. 

The  medulla  receives  its  blood  from  the  concave  surface  of  the 
arterial  arch.  The  arterioles  given  off  have  a  straight  course,  and 
are  the  arteriolae  rectae.  They  very  soon  break  up  into  capillaries 
that  surround  the  tubules  of  the  medulla.  Huber  and  others  state 
that  some  of  the  arteriolae  rectae  are  derived  from  the  efferent  glomer- 
ular arterioles  nearest  the  medulla.  These  are  the  arlerice  recta 
spuria  and  possess  no  circular  muscle  fibers.  They  proceed  in  the 
same  manner  as  the  true  arteriae  rectae.  These  continue  as  venous 
radicals  that  unite  to  form  straight  veins,  venae  rectae,  which  empty 
into  the  venous  arch  on  its  concave  surface. 

The  venous  arches  unite  at  the  columns  of  Bertin,  and  pass 
down  these,  parallel  to  the  arteries,  as  the  interlobar  veins.  In  the 
sinus,  they  unite  to  form  the  renal  vein. 

In  addition  to  the  branches  from  the  renal  artery  the  capsule  also 
receives  many  branches  from  neighboring  arteries  and  these  anas- 
tomose with  the  end  branches  of  the  interlobular  arteries.  The 
vessels  of  the  kidney,  therefore,  communicate  with  those  of  the 
perirenal  fat,  through  the  vessels  of  the  capsule.  This  is  of  impor- 
tance surgically.  Direct  anastomoses  between  arterial  and  venous 
vessels  occur  in  this  organ. 

The  lymphatics  of  the  kidney  comprise  a  capsular  sety  cortical  and 
medullary  plexuses.  The  capsular  vessels  receive  lymph  from  the 
capsule  and  perirenal  fat  and  the  efferents  convey  the  lymph  partly 
to  the  deep  set  and  partly  to  the  lymph  nodes  of  the  lumbar  region. 
The  cortical  vessels  form  a  plexus  in  the  interstitial  tissue,  receive 
some  of  the  lymph  from  the  capsular  region  and  pass  the  lymph  to 
the  medullary  plexus.  The  latter  receives  the  lymph  from  the 
cortex  and  from  the  plexus  of  vessels  in  the  interstitial  tissue  of  the 
medulla  and  the  efferents  convey  the  lymph  to  the  hilus  and  from 
there  to  the  neighboring  lymph  nodes.  These  lymph  channels 
accompany  the  vessels  and  are  irregular  in  caliber. 

The  nerves  are  derived  from  both  systems.  They  follow  the 
vessels  and  in  the  sinus  form  a  plexus  around  the  pelvis  of  the  ureter, 
containing  ganglia.  The  nerves  follow  the  vessels  and  envelop 
them  in  networks  to  the  smallest  divisions.     Some  of  these  nerves 


3 $6  PRACTICAL  HISTOLOGY 

supply  the  muscles  of  the  vessels  and  others  pass  to  the  tubules 
where  their  terminal  fibers  pass  through  the  basement  membrane 
and  end  between  the  cells  in  small  knob-like  terminals. 

The  kidney  is  the  organ  that  excretes  the  urine.  The  liver  is  the 
organ  that  makes  the  urea  which  is  then  carried  to  the  kidney  to 
be  excreted.  The  urine  contains  urea,  uric  acid,  urates  and  inor- 
ganic salts  such  as  chlorids,  sulphates,  and  phosphates  of  sodium, 
potassium  and  calcium  all  dissolved  or  suspended  in  the  water.  The 
color,  reaction  and  specific  gravity  will  depend  upon  the  amount  of 
the  solids  and  the  proportion  of  wrater.  As  the  blood  courses  through 
the  capillaries  of  the  cortical  portion  of  the  kidneys  the  columnar 
cells  of  the  convoluted  tubules  remove  the  salts  by  a  "selective 
power"  and  transfer  them  to  the  lumen  of  the  tubule.  Through 
the  capsule  of  Bowman  and  the  walls  of  the  descending  limb  of 
Henle's  loop  in  cortex  and  medulla,  the  water  diffuses  or  osmoses 
and  passing  down  the  tubules  dissolves  and  carries  along  the  solids. 
If  the  water  is  in  sufficient  quantity  these  are  all  dissolved.  If  the 
water  is  not  sufficient  the  more  insoluble  salts,  like  uric  acid,  will 
be  only  partly  dissolved  and  the  remainder  will  be  present  in  the 
form  of  a  sediment.  Sometimes  these  salts  form  urinary  concretions 
in  the  kidney  or  the  bladder.  Such  concretions  are  readily  seen 
in  the  cells  of  the  convoluted  tubules  of  reptiles,  birds  and  some 
mammals.  In  addition  epithelial  cells  are  present  in  the  urine  and 
even  casts  of  the  tubules  are  found.  The  cells  of  the  different  parts 
of  the  tubule  are  readily  recognized. 

THE  EFFERENT  APPARATUS 

The  efferent  apparatus  consists  of  the  pelvis,  ureter,  bladder  and 
urethra. 

The  pelvis  is  the  upper,  expanded  portion  of  the  ureter,  and  lies  in 
the  sinus.  It  is  very  irregular,  and  is  divided  into  two  or  three  main 
portions,  the  infundibula,  or  calices  major,  which  are  arranged 
in  little  cup-like  structures  around  the  apices  of  medullary  pyramids. 
The  latter  are  the  calices  minor,  and  they  are  not  equal  in  number 
to  the  pyramids  as  one  calix  surrounds  the  apices  of  two  or  three 
pyramids.  The  three  coats,  mucous,  muscular  and  fibrous,  extend 
throughout  the  ureter  and  bladder. 


THE    URINARY    SYSTEM  337 

The  mucous  membrane  consists  of  transitional  cells,  basement 
membrane  and  tunica  propria.  In  the  calyces  minores  the  epithelium 
is  of  the  simple  columnar  variety  and  is  continuous  with  the 
same  kind  that  coYers  the  apices  of  the  Malpighian  pyramids  and 
lines  the  papillary  ducts.  The  epithelial  cells  of  the  remainder  of 
the  pelvis  are  of  the  transitional  variety.  The  superficial  cells  are 
somewhat  flattened  and  almost  squamous.  Just  beneath  these 
the  cells  are  somewhat  larger  and  pear-shaped  while  the  deepest 
(basal  cells)  are  polyhedral.  These  deeper  cells  divide  by  karyo- 
kinesis  and  these  daughter  cells  replace  the  superficial  cells  as  they 
desquamate.     The  superficial  cells  divide  by  the  direct  method. 

The  tunica  propria  consists  of  fibro-elastic  areolar  tissue  in  which 
there  may  be  some  diffuse  lymphoid  tissue.  On  the  epithelial 
side  it  is  papillated  and  very  vascular.  The  capillaries  may  extend 
even  into  the  deeper  parts  of  the  epithelial  layer.  Racemose 
glands  are  said  to  occur  in  the  mucosa  but  Shafer  denies  their 
presence. 

The  muscular  coat  consists  of  smooth  muscle  tissue  that  is  not 
arranged  in  distinct  layers.  Bundles  of  muscle  fibers  extend  into 
the  fibrous  coat. 

The  fibrous  coat  is  a  thin  supportive  layer  of  white  fibrous  con- 
nective tissue.  Its  fibers  connect  with  those  of  the  areolar  tissue 
of  the  sinus  and  at  the  lines  of  reflection  of  the  calyces  minores  upon 
the  apices  of  the  Malpighian  pyramids  this  fibrous  tissue  blends  with 
the  interstitial  tissue  of  the  kidney. 

At  the  caudal  extremity  of  the  sinus  the  pelvis  becomes  drawn 
into  a  small  tube  that  is  the  ureter. 

URETER 

The  ureter  is  the  small  tube  connecting  the  kidney  and  the 
bladder,  which  organ  it  enters  at  an  acute  angle.  Its  coats  are 
quite  distinct  and  are  mucous,  muscular  and  fibrous. 

The  mucosa  resembles  that  of  the  pelvis  with  which  it  is  contin- 
uous. The  epithelial  cells  are  of  the  transitional  variety  and  are 
arranged  in  four  layers;  the  two  basal  layers  are  rounded  or  ovoid 

in  form,   the   third  layer  somewhat  pear-shaped  and  the  super- 
22 


338 


PRACTICAL   HISTOLOGY 


ficial  cells  are  large  and  cuboid  in  form,  in  the  resting  condition  of 
the  duct.  Intercellular  bridges,  or  processes  connect  the  various 
cells  together.  The  superficial  cells  may  show  two  nuclei,  a  cuticular 
border  is  usually  present  and  the  cells  usually  divide  by  the  direct 
method.  When  the  tube  is  distended  with  urine  then  the  cells  be- 
come flattened  temporarily.  The  tunica  propria  often  sends  delicate 
fibers  into  the  deeper  layers  of  the  epithelium  and  capillaries  may  even 


Fig.  200. 
A,  Cross-section  of  Human  Ureter — a,  Lumen;  b,  epithelium;  c,  basement  mem- 
brane; d,  longitudinal  fold  of  mucosa;  e,  tunica  propria;/,  inner  longitudinal 
muscle;  g,  outer  circular  muscle;  h,  vessels;  i,  fibrous  coat.  B,  Cross-sec- 
tion of  Segment  of  Human  Bladder — a.  Mucous  coat;  b,  muscular  coat; 
c,  fibrous  coat;  d  transitional  epithelium;  e,  basement  membrane;/,  tunica 
propria;  g,  blood-vessels;  h,  white  fibrous  tissue;  i,  inner  longitudinal  muscle; 
k,  middle  circular  muscle;  I,  white  fibrous  tissue;  m,  outer  longitudinal 
muscle;  n,  venule;  o,  arteriole;  p,  adipose  tissue. 

be  present  here.  The  basement  membrane  is  thin  and  is  pierced  by 
the  fibers  mentioned  above.  The  tunica  propria  consists  of  areolar 
tissue  that  is  looser  near  the  muscle  coat.  In  it  are  found  some  dif- 
fuse lymphoid  tissue  and  even  solitary  nodules;  in  lower  animals 
small  racemose  glands  of  the  mucous  type  are  also  present.  This 
mucosa  is  thrown  into  longitudinal  folds  in  the  empty  condition 
of  the  tube  and  the  lumen  then  is  small  and  stellate  in  shape. 


THE   URINARY   SYSTEM  339 

The  muscle  coat  consists  of  smooth  muscle  tissue  arranged  in 
definite  layers.  In  the  bulk  of  the  ureter  there  are  two  layers, 
inner  longitudinal  and  outer  circular.  The  longitudinal  layer  is 
best  developed  in  the  first  part  of  the  tube  and  in  the  middle  portion 
the  circular  fibers  are  most  marked;  in  the  lower  part  and  outer 
longitudinal  layer  is  added  and  this  is  well  developed.  Although 
this  layer  seems  to  be  derived  from  the  musculature  of  the  bladder 
but  it  belongs  distinctly  to  the  ureter  and  is  called  the  ureter -sheath, 
by  Waldeyer.  This  layer  is  distinctly  separated  from  the  middle 
circular  layer  and  from  the  fibrous  coat.  The  muscle  coat  has  a 
considerable  quantity  of  areolar  tissue  between  the  muscle  bundles. 

The  fibrous  coat  is  a  thin,  distinct  layer  of  white  fibrous  tissue 
that  surround  the  tube.  Even  in  that  part  of  the  ureter  that  passes 
through  the  bladder  wall  this  coat  maintains  its  identity  and  at  the 
terminal  part  of  the  ureter  blends  with  the  fibrous  portion  of  the 
mucosa. 

At  the  ureteral  orifice  in  the  bladder  the  mucosa  becomes  con- 
tinuous with  that  of  the  bladder.  At  this  region  the  mucosa  of  the 
ureter,  at  the  upper  part  of  the  orifice,  projects  in  the  form  of  a 
small  fold  called  the  valve  of  the  ureter. 

The  blood-vessels  of  the  ureter  are  numerous.  The  arterial 
vessels  pass  into  the  fibrous  coat  and  from  these  capillaries  pass  to 
the  superficial  parts  of  the  mucosa  and  glands  and  to  the  muscle 
coat.  This  blood  is  collected  by  the  venous  channels  that  have  a 
corresponding  course  and  then  empty  in  the  neighboring  veins. 

The  lymph  from  the  interstitial  spaces  is  carried  to  plexuses  of 
vessels  that  lie  in  the  mucous,  muscular  and  fibrous  coats;  these 
plexuses  communicate  with  one  another  and  the  lymph  is  ultimately 
carried  to  the  plexus  in  the  fibrous  coat;  from  here  it  is  carried 
by  efferent  channels  to  the  neighboring  lymph  nodes. 

The  nerves  are  from  the  sympathetic  system  and  they  form  a 
ganglionated  plexus  in  the  fibrous  coat.  The  sensor  fibers  form  a 
plexus  in  the  tunica  propria  and  from  this  some  fibers  terminate 
in  the  deeper  epithelial  layers  while  others  terminate  in  the  areolar 
tissue  in  tufts  of  fine  fibrils.  The  motor  fibers  pass  to  the  muscle 
tissue  of  the  tube  and  to  the  muscle  of  the  vessels. 


340  PRACTICAL   HISTOLOGY 

BLADDER 

The  bladder  is  a  muscular  sac  that  acts  as  a  reservoir  for  the 
urine.  It  consists  of  fundus  or  body,  and  a  small  constricted  por- 
tion, the  neck,  which  continues  as  the  urethra. 

The  mucous  coat  resembles  that  of  the  ureter  in  structure. 
The  transitional  cells  vary  according  to  the  state  of  the  bladder. 
When  this  organ  is  empty  and  contracted  the  cells  are  of  the  transi- 
tional variety.  When  the  bladder  is  distended  the  surface  cells 
flatten  in  order  to  assist  in  covering  the  extended  surface.  The 
superficial  cells  reproduce  by  amitosis  and  the  deeper  ones  by  mitosis. 
In  urinary  examination  it  is  impossible  to  tell  the  cells  of  the  pelvis, 
ureter  and  bladder  from  one  another.  The  tunica  propria  consists 
of  areolar  tissue  and  contains  some  lymphoid  tissue  of  the  diffuse 
variety  and  even  solitary  nodules.  Mucous  glands  are  said  by  some 
to  be  present  while  others  deny  their  presence.  These  so-called 
glands  are  probably  evaginations  of  the  epithelium  that  may  be 
solid  or  hollow.  As  a  basement  membrane  seems  to  be  absent,  delicate 
fibrils  of  the  tunica  propria  and  even  capillaries  are  sometimes  seen 
in  the  deeper  layers  of  the  epithelium. 

The  mucosa  is  of  a  reddish-pink  color  (due  to  the  vascularity) 
soft  and  loosely  attached  to  the  muscle  coat  except  at  the  trigone; 
this  triangular  area  has  for  its  apex  the  urethral  orifice  and  for  its 
basal  angles  the  ureteral  orifices.  A  line  connecting  the  two  orifices 
of  the  ureters  is  the  base  and  this  area  is  the  trigonum  vesica.  In  the 
empty  and  partially  distended  condition  the  mucosa  is  thrown  into 
folds,  except  at  the  trigone,  that  are  the  rugce  of  the  bladder.  These 
gradually  smooth  out  under  distension  and  when  the  organ  is  fully 
distended  the  mucosa  is  even.  In  all  of  the  hollow  organs  that 
undergo  considerable  distension  this  is  the  case. 

The  muscle  coat  is  composed  of  smooth  muscle  tissue  but  the 
layer  formation  is  not  so  distinct  as  in  the  ureter.  Three  layers  are 
described,  inner  longitudinal,  middle  circular  and  outer  longitudinal. 
The  inner  longitudinal  layer  is  described  by  some  as  belonging  to 
the  submucosa  of  the  bladder  as  it  is  separated  from  the  middle 
circular  layer  by  a  narrow  band  of  areolar  tissue,  the  so-called 
submucosa.  These  muscle  fibers  are  really  irregular  scattered  and 
do  not  form  a  distinct  longitudinal  layer.     At  the  fundus  of  the 


Till-;    URINARY    SYSTEM 


341 


bladder  there  is  an  additional  layer  of  smaller  and  finer  fibers  called 
the  submucous  muscle  layer.  They  probably  represent  a  partially 
developed  muscularis  mucosae  and  form  the  internal  sphincter  muscle 
of  the  bladder. 

The  middle  circular  fibers  are  not  arranged  in  a  distinct  transverse 
manner  but  form  a  network  especially  in  the  upper  part  of  the  organ. 
In  the  lower  part  they  are  more  distinctly  circularly  arranged  and 
at  the  base  of  the  bladder  they  disappear.  Their  place  is  taken  by 
the  submucous  layer  previously  mentioned.  The  circular  layer  is 
thicker  than  the  outer  longitudinal  layer. 

The  outer  longitudinal  fibers  form  a  distinct  layer  on  the  ventral 
and  dorsal  surfaces  of  the  organ;  at  the  sides  these  fibers  are  more 
oblique  in  direction  and  interlace  somewhat. 

The  fibrous  coat  is  quite  thin  and  poorly  developed  over  the 
greater  part  of  the  bladder.  Its  fibers  extend  in  between  the  muscle 
bundles  and  join  the  considerable  white  fibrous  tissue  of  the  muscle 
coat.  About  one-half  of  the  bladder  has  a  serous  covering  that 
represents  a  reflection  of  the  peritoneum  over  the  organ. 

The  muscular  coat  is  so  irregular  in  its  thickness  that  in  the  dis- 
tended organs  parts  of  the  wall  are  very  thin.  If  these  areas  become 
so  weak  as  to  permit  the  mucosa  and  fibrosa  to  bulge  the  bladder 
becomes  sacculated  and  the  projections  are  each  known  as  an 
appendix  vesica. 

The  bladder  receives  its  blood-supply  from  the  superior  and  in- 
ferior vesical  arteries  and,  in  the  female  the  uterine  artery  sends 
branches.  These  vessels  form  a  network  in  the  fibrous  coat  and 
from  this  branches  extend  to  the  muscle  coat  to  form  an  extensive 
capillary  plexus;  other  branches  pass  to  the  mucous  (submucous 
of  some)  and  form  a  plexus  here,  the  branches  of  which  supply  the 
mucous  coat.  The  blood  is  then  collected  into  venous  channels 
that  form  plexuses  that  are  located  in  the  three  coats,  with  the 
exception  of  the  trigone  area.  From  these  plexuses  veins  arise 
that  carry  the  blood  to  the  internal  iliac  veins,  but  do  not  accompany 
the  arteries. 

The  lymphatic  vessels  are  found  in  the  muscle  and  fibrous  coats 
and  the  trigone  of  the  mucosa.  The  lymph  of  the  intercellular 
spaces  is  carried  to.  these  plexuses,  the  muscle  plexus  emptying  into 


342 


PRACTICAL   HISTOLOGY 


the  plexus  in  the  fibrous  coat.     The  efferents  from  the  fibrous  coat 
carry  the  lymph  to  the  neighboring  nodes. 

The  nerves  are  both  cerebrospinal  and  sympathetic.  The  former 
are  motor  from  the  third  and  fourth  sacral  spinal  nerves  chiefly 
and  sensor  from  the  twelfth  thoracic  and  first  and  second  lumbars; 
the  sympathetic  nerves  are  from  the  hypogastric  plexus.  Both 
sets  of  fibers  go  to  the  pelvic  plexus  and  from  this  other  fibers  pass 
to  the  bladder  and  form  the  vesical  plexus.  From  this  each  half 
of  the  bladder  is  supplied  independently.  In  the  fibrous  coat  there 
are  ganglia  that  are  more  numerous  near  the  base  of  the  bladder; 
fibers  from  these  ganglia  form  a  fine  plexus  in  the  muscle  coat  and 
the  terminal  fibers  of  this  plexus  supply  the  muscle  fibers.  There 
is  another  fine  plexus  in  the  mucous  coat,  fibers  from  which  supply 
the  neighboring  muscle  fibers  and  the  epithelium  of  the  deeper 
layers. 

THE  FEMALE  URETHRA 

The  female  urethra  consists  of  two  coats,  mucous  and  muscular. 
This  tube  is  shorter  and  of  a  wider  caliber  than  in  the  male. 

The  mucosa  consists  of  epithelium  that  is  of  two  varieties;  at 
the  beginning  of  the  tube  the  transitional  cells  of  the  bladder  continue 
into  it  and  are  somewhat  flattened.  As  the  external  urinary  meatus 
is  approached  the  epithelium  changes  to  the  stratified  squamous 
variety  that  is  continuous  with  that  of  the  vestibule.  Some  de- 
scribe a  stratified  columnar  variety  in  the  middle  part  of  the  tube. 
These  cells  rest  upon  the  tunica  propria  that  is  usually  papillated 
and  also  thrown  into  longitudinal  folds.  In  the  areolar  tissue  are 
found  a  few  racemose  mucous  glands,  the  glands  of  Littre.  Some 
tubular  glands  may  be  present  near  the  bladder  and  these  will 
contain  structures  that  resemble  the  amyloid  bodies  of  the  male 
prostate  gland.  Near  the  external  orifice  are  seen  the  ducts  of  the 
periurethral  glands.  The  outer  part  of  the  tunica  propria  is  loose 
and  contains  many  large  calibered  venous  channels  that  constitute 
erectile  tissue  sometimes  called  the  corpus  spongiosum  urethra?-. 

The  muscle  coat  consists  of  smooth  muscle  tissue  arranged  into 
incomplete  outer  circular  and  inner  longitudinal  layers  separated 
from  each  other  by  an  intermuscular  layer  of  white  fibrous  tissue. 


THE    URINARY    SYSTEM  343 

The  longitudinal  fibers  are  best  marked  at  the  distal  end  of  the  ure- 
thra and  in  the  dorsal  wall;  the  circular  fibers  are  best  marked  at 
the  proximal  extremity  where  they  tend  to  form  an  indistinct  sphinc- 
ter muscle.  Some  voluntary  striated  fibers  are  found  in  this  muscle 
coat. 

THE  MALE  URETHRA 

The  male  urethra  is  more  complex  and  differs  in  function  from  that 
of  the  female  in  not  only  carrying  the  urine  but  also  the  genital 
secretions.  It  is  18  to  20  cm.  in  length  and  is  divided  into  three 
parts,  prostatic,  membranous  and  penile  portions.  The  prostatic 
part  lies  within  the  prostate  gland  and  measures  about  3  cm.  in 
length  and  in  the  resting  condition  the  mucosa  is  thrown  into 
longitudinal  folds.  It  is  the  least  distensible  part  of  the  tube. 
Along  the  dorsal  wall  is  a  permanent  ridge  called  the  urethral  crest 
and  on  each  side  there  is  a  longitudinal  groove  called  the  prostatic 
sinus  in  which  are  seen  the  numerous  openings  of  the  ducts  of  the 
prostatic  glands.  In  the  urethral  crest  there  are  three  openings 
side  by  side;  the  middle  one  is  the  largest  and  represents  the  orifice 
of  the  prostatic  utricle. 

This  is  a  blind  pouch,  the  remnants  of  the  fused  distal  extremities 
of  the  fetal  ducts  by  Miiller,  representing  the  vagina  of  the  female. 
This  sac  is  from  6  to  12  mm.  deep  and  is  lined  with  simple  columnar, 
or  according  to  some  simple  ciliated  cells.  These  rest  upon  a  basement 
membrane  outside,  of  which  is  the  tunica  propria  that  contains  con- 
siderable true  erectile  tissue  and  some  smooth  muscle  fibers  that  are 
continuous  with  that  of  the  urethral  crest.  In  the  side  walls  are 
the  ejaculatory  ducts  and  near  the  urethral  orifice  are  some  small 
glands  that  empty  into  the  cavity  of  the  sinus.  It  is  said  that  when 
the  crest  is  engorged  with  blood  it  prevents  the  passage  of  the  semen 
backward  into  the  bladder  (Walker).  On  each  side  of  the  orifice 
of  the  utricle  is  seen  the  opening  of  each  ejaculatory  duct. 

The  membranous  part  of  the  urethra  is  about  18  mm.  in  length 
and  lies  between  the  layers  of  the  triangular  ligament.  It  connects 
the  prostatic  and  spongy  portions.  It  is  the  narrowest  part  and 
has  the  thinnest  walls  and  is  therefore  most  liable  to  rupture  through 
the  improper  passage  of  urethral  instruments.     It  is  surrounded  by 


344  PRACTICAL   HISTOLOGY 

smooth  muscle  and  erectile  tissues  and  upon  each  side  is  a  gland  of 
Cowper.     On  section  the  lumen  is  stellate. 

The  penile,  or  spongy  portion  is  about  15  cm.  in  length  and  lies 
in  the  corpus  spongiosum  of  the  penis  and  is,  therefore,  surrounded 
by  erectile  tissue.  Its  caliber  varies  in  its  different  parts  and  at 
its  distal  extremity,  just  within  the  external  urinary  meatus  it  is 
markedly  dilated;  this  constitutes  the  fossa  navicular  is.  In  section 
the  lumen  is  X-shaped. 

The  mucosa  consists  of  epithelium,  basement  membrane  and 
tunica  propria.  The  epithelium  of  the  tree  parts  varies  and  although 
the  following  is  a  general  description,  variations  are  met  with. 
In  the  prostatic  part  the  cells  are  of  the  transitional  type  continued 
from  the  bladder.  These  cover  the  urethral  crest  and  continue 
into  the  prostatic  sinuses  and  ducts  of  the  prostatic  glands  for  a 
short  distance.  In  the  membranous  part  the  epithelium  changes 
to  the  stratified  columnar  type.  In  the  penile  part  most  of  the  cells 
are  of  the  simple  columnar  variety,  but  the  fossa  navicularis  is  lined 
with  stratified  squamous  cells  that  are  continuous  with  those  upon 
the  surface  of  the  glans  penis.  Goblets  cells  are  also  present.  These 
cells  rest  upon  a  delicate  basement  membrane  that  is  supported  by 
the  areolar  tunica  propria  in  which  the  elastic  fibers  are  very  numer- 
ous. This  layer  contains  near  the  outer  part,  many  anastomosing 
veins  that  connect  with  the  cavernous  spaces  in  the  corpus  spon- 
giosum. In  the  tunica  propria  there  are  many  small  glands  of  the 
mucous  type,  these  are  the  urethral  glands,  or  glands  of  Littre.  In 
addition  there  are  many  outpouchings  of  the  mucosa  forming  the 
lacunae  the  largest  of  which  is  in  the  fossa  navicularis  and  is  called 
the  lacuna  magna. 

The  muscle  tissue  is  of  the  smooth  variety.  In  the  prostatic 
part  the  outer  circular  fibers  are  predominant  and  near  the  bladder 
end  tend  to  form  a^sphincter.  These  fibers  connect  with  the  mus- 
culature of  the  prostate.  The  inner  longitudinal  layer  is  thin  and 
continues  into  the  membranous  and  penile  portions.  In  the  mem- 
branous part  the  muscle  coat  is  thin  and  is  reinforced  by  voluntary 
striated  fibers  that  represent  the  compressor  urethra  muscle.  This 
tapers  toward  the  prostatic  and  penile  portion.  In  the  penile  part 
the  muscle  is  all  smooth  and  is  found  chiefly  in  the  dorsal  and 


I  UK    URINARY    SYSll.M  345 

lateral  walls.  It  is  mainly  longitudinally  directed  and  disappears 
before  the  glans  is  reached. 

The  blood-vessels  are  numerous.  The  arteries  give  off  branches 
some  of  which  form  capillaries  in  the  usual  way;  other  branches 
are  tortuous  and  gradually  pass  over  into  large  dilated  endothelial 
walled  channels  that  are  called  sinuses  and  constitute  the  true 
erectile  tissue.  These  are  extensive  cavernous  spaces  that  lead  into 
venules  that  conduct  the  blood  from  the  organ.  The  ordinary 
capillaries  supply  the  mucosa  and  the  muscle  tissue. 

The  lymphatic  vessels  of  the  urethra  are  chiefly  in  the  mucosa; 
these  receive  the  lymph  from  the  interstitial  spaces  and  the  efferents 
carry  the  lymph  to  the  abdominal  nodes. 

The  nerves  are  derived  from  those  of  the  clitoris  or  penis.  They 
are  both  cerebrospinal  and  sympathetic.  The  cerebrospinal  are 
motor  and  sensor,  the  motor  going  to  the  voluntary  muscle  and  the 
sensor  to  the  epithelium  of  the  mucosa  as  free  endings  and  to  the 
tunica  propria  where  the  fibers  terminate  in  the  genital  corpuscles 
and  Pacinian  bodies.  The  sympathetic  fibers  from  the  hypogastric 
plexus  pass  to  the  smooth  muscle  tissue  of  the  vessels  and  the  muscle 
coat  of  the  urethra. 

The  various  portions  of  the  urinary  system  are  lined  by  the  follow- 
ing cells: 

Kidney. 

Urinlferous  Tubule: 

Renal  Corpuscle Simple  squamous. 

Neck Simple  squamous. 

First  Convoluted  Tubule  ....   Cuboidal  to  columnar. 

Descending  Limb Simple  squamous. 

Loop  of  Henle Simple  squamous  or  low  cuboidal. 

Ascending  Limb Low  cuboidal. 

Second  Convoluted  Tubule   .    .    .   Cuboidal  to  columnar. 

Arched  Connecting  Tubule  .    .    .   Cuboidal. 

Straight  Collecting  Tubule.    .    .   Columnar. 

Papillary  Ducts Tall  columnar. 

Pelvis Transitional. 

Ureter Transitional. 

Bladder Transitional. 

TT  „  J  Transitional. 

Urethra.    Female <  _,      ... 

^  Stratified  squamous. 


346  PRACTICAL  HISTOLOGY 

Male 

First  Part  (Prostatic) Transitional. 

Second  Part  (Membranous)    .    .    .  Stratified  columnar. 

Third  Part  (Spongy)     ......  Simple  columnar. 

Fossa  Naviculars Stratified  squamous. 

ADRENAL 

The  adrenal,  or  suprarenal  body  is  a  ductless  gland.  It  lies  at 
the  upper  pole  of  the  kidney,  and  is  yellowish  in  color.  Upon 
section,  it  shows  a  yellow  external  layer,  and  a  dark  centrum.  Upon 
the  ventral  surface  of  each  gland  is  an  indentation  called  the  hilus 
which  permits  the  exit  of  several  veins. 

The  organ  is  surrounded  by  a  capsule  of  white  fibrous  connective 
tissue  that  contains  a  considerable  quantity  of  smooth  muscle  tissue. 
From  the  internal  surface  of  the  capsule  trabecular  extend  into  the 
organs  and  anastomosing  form  the  coarse  framework  of  the  structure. 
These  trabecular  contain  some  smooth  muscle  tissue.  Within  the 
network  formed  by  the  trabecular  there  is  a  delicate  meshwork  of 
reticulum  that  constitutes  the  finer  framework  and  this  supports  the 
functionating  epithelium,  blood-vessels,  nerves  and  lymph  channels. 
This  reticulum  is  connected  to  and  derived  from  the  trabecular 
framework.  The  arrangement  of  the  trabecular  differs  in  the 
various  parts  of  the  organ.  Just  beneath  the  capsule  the  trabecular 
anastomose  at  short  intervals  forming  spaces  that  are  approximately 
from  0.0125  to  0.02  mm.  in  diameter  so  that  the  epithelial  cells  are 
arranged  here  in  ball-like  masses  constituting  the  zona  glomerulosa. 
In  some  areas  these  glomeruli  are  wanting  perhaps  because  the 
trabecular  failed  to  form  these  spaces.  Just  within  this  zone  the 
trabecular  are  straight  and  parallel  to  one  another  causing  the  cells 
to  arrange  themselves  in  columns,  two  cells  wide.  This  is  the  zona 
fasciculata  and  is  the  widest  zone  of  the  cortex.  At  the  end  of  this 
zone  the  trabecular  again  anastomose  freely  but  irregularly  so  that 
the  meshes  here  are  more  variable  in  extent  and  more  irregular 
than  in  the  glomerular  zone.  The  cells  in  this  inner  zona  reticularis 
are  therefore  arranged  into  anastomosing  chains  and  form  the 
narrowest  and  least  distinct  zone  of  the  cortex.  In  the  central 
part  of  the  organ,  the  medulla,  the  trabecular  arrangement  is  the 


THE    URINARY   SYSTEM  347 

most  irregular  of  all.  Here  they  course  and  anastomose  in  such  a 
manner  that  some  in  places  chains,  in  others  glomeruli  and  groups 
are  formed.  In  the  stroma  of  the  medulla  considerable  elastic 
tissue  is  said  to  occur. 

The  peripheral  portion  of  the  organ  is  the  cortex  and  the  arrange- 
ment of  the  parenchyma  into  its  three  zones  is  due  to  the  direction 
taken  by  the  trabecule.  The  divisions  are  the  zona  glomerulosa, 
zona  fasciculata  and  zona  reticularis. 

The  zona  glomerulosa  consists  of  groups  of  cells  that  measure 
from  0.0125  to  0.02  mm.  in  diameter.  These  groups  may  be 
spheroidal,  or  somewhat  curved  in  form  and  this  zone  is  two  or  three 
glomerules  wide.  In  some  places,  however,  the  glomerules  are 
absent  and  the  zona  fasciculata  comes  to  the  capsule.  The  groups 
are  fairly  widely  separated  from  one  another  the  intervening  spaces 
being  filled  in  with  the  trabecular,  reticulum  and  the  capillaries. 
The  cells  are  mainly  polyhedral,  12  to  20  microns  in  diameter,  but 
in  some  animals  they  are  columnar  in  shape  and  a  central  lumen 
may  be  apparent.  The  outlines  of  the  cells  are  usually  not  distinct; 
the  cytoplasm  contains  a  large  number  of  fine  acidophilic  granules 
and  quite  a  few  droplets  of  fat  that  assist  in  giving  the  yellowish 
color  to  the  cortex.     The  spherical  nuclei  are  rich  in  chromatin. 

The  zona  fasciculata  consists  of  comparatively  long  columns  of 
cells  that  form  the  widest  zone  of  the  cortex.  The  cells  of  the 
innermost  glomeruli  may  be  continuous  with  the  column  cells. 
These  columns,  two  cells  wide,  consist  of  polyhehral,  or  columnar 
cells,  whose  cell  outline  is  distinct.  In  some  cells  the  spherical  nuclei 
are  vesicular  and  in  others  they  contain  considerable  chromatin. 
This  condition  seems  to  be  in  relation  with  the  structure  of  the 
cytoplasm.  In  some  columns  the  cytoplasm  of  the  cells  is  finely 
granular  (acidophilic)  and  the  droplets  of  fat  are  extremely  small. 
In  such  cells  the  nucleus  (there  may  be  two)  are  usually  darkly 
staining.  In  other  columns  all  of  the  cells  show  the  cytoplasm  to 
contain  but  few  granules  while  the  fat  droplets  are  numerous  and 
large.  The  nuclei  are  usually  pale  and  vesicular.  The  cell  outline 
not  quite  so  distinct  as  in  the  other  cells. 

The  zona  reticularis  consists  of  anastomosing  chains  of  cells  and 
although  of  the  general  form  and  size  of  the  preceding  differ  in 


348 


PRACTICAL   HISTOLOGY 


structure.  The  nucleus  contains  considerable  chromatin  while  the 
cytoplasm  contains  very  little  fat.  On  the  other  hand  the  cytoplasm 
contains  a  large  number  of  coarse  granules  of  pigment.  These 
granules  are  yellowish  brown  and  are  said  to  be  present  only  in  the 
adolescent  and  adult  condition  and  also  said  to  vary  in  different 
individuals.     These  are  chromaffin  granules. 

In  the  fetus  and  at  birth  the  large  size  of  the  adrenals  is  due  to  the 
excessive  development  of  the  inner  part  of  the  cortex.     The  cells 


Fig.  201. — Section  of  Human  Adrenal. 

o,  Capsule;  b,  zona  glomerulosa;  c,  zona  fasciculata;  d,  zona  reticularis;  e,  chrom- 
affin cells  of  the  medulla;  /,  medullary  vein. 

contain  no  fat  and  this  part  is  very  vascular.  This  fetal  cortex 
begins,  shortly  after  birth,  to  show  fatty  degeneration  of  its  cells  so 
that  by  the  end  of  the  first  year,  usually,  it  is  gone.  The  per- 
ipheral cells,  however,  are  fat  containing  and  form  a  very  thin  layer. 
From  this  the  cortex,  as  seen  later,  is  developed. 

The  medulla  consists  of  epithelial  cells  that  resemble  those  of  the 
zona  reticular  closely.  They  are  different  in  size  and  the  smaller 
ones  are  arranged  in  anastomosing  columns  while  the  larger  ones 
are  arranged  in  groups.     The  smaller  cells  contain  more  fat  and  the 


THE    URINARY    SYSTEM 


349 


nuclei  do  not  stain  so  deeply.  The  large  cells  arc  polyhedral,  their 
cytoplasm  is  finely  granular  (acidophilic)  and  the  nuclei  stain  more 
readily.  They  are  said  to  contain  secretory  canaliculi.  In  these 
cells  there  are  also  granules  like  those  found  in  the  cells  of  the 
reticularis.  These  chromaffin  granules  are  supposed  to  be  connected 
with  the  formation  of  the  adrenalin  and  they  stain  deeply  with 
chromium  salts.  These  granules  are  also  found  in  the  hypophysis. 
In  the  reticulum  of  the  medulla  in  addition  to  the  blood-vessels 
isolated  sympathetic  nerve  cells  and  small  ganglia  are  found. 


Fig.  202. — Fat  Globules  in  the  Cells  of  the  Zona  Glomerulosa  of  the 
Adrenal  Gland  Fixed  inOsmic  Acid.     (Photograph.  Obj.  16  mm.,  oc.  10  x.) 


The  arteries  are  from  several  sources  and  their  branches  form  a 
plexus  of  vessel  in  the  capsule  of  the  organ.  Some  of  the  branches 
of  this  plexus  supply  the  capsule;  others,  the  cortical  arteries,  soon 
form  a  dense  plexus  of  capillaries  of  the  sinusoidal  type  around  the 
cells  of  the  various  zones.  The  endothelium  of  the  capillaries  is  in 
direct  contact  with  the  epithelium  of  the  organ  as  in  the  liver.  In 
the  reticularis  the  sinusoids  are  larger  and  their,  anastomoses  more 
frequent  and  from  this  plexus  venules  arise  that  pass  directly  to  the 
central  veins  of  the  medulla.  Other  branches  from  the  capsular 
plexus  are  the  medullary  arteries.  These  pass,  without  branching, 
through  the  cortex  straight  to  the  medulla  where  they  form  a  mesh- 
work  of  sinusoids  around  the  cell-groups.  In  some  places,  it  is 
said,  the  endothelium  is  absent  and  the  medullary  cells  are  bathed 


350  PRACTICAL  HISTOLOGY 

directly  in  blood.  The  presence  of  the  sinusoids,  especially  those 
of  the  open  type,  facilitates  the  transfer  of  the  internal  secretion, 
adrenalin,  from  the  cells  directly  to  the  blood.  It  is  also  stated 
that  diverticula  of  the  sinusoids  penetrate  the  cell  chains  and  groups. 
From  the  medullary  plexus  of  sinusoids  the  blood  is  collected  by  a 
few  venules  that  ultimately  unite  to  form  the  two,  to  four  medullar y 
veins.  These  leave  the  organ  at  the  hilus.  The  veins  of  the  capsule 
do  not  join  the  central  veins. 

Lymph  vessels  are  numerous.  One  plexus  lies  in  the  medulla  and 
another  in  the  capsule.  These  two  are  connected  by  vessels  that 
pass  through  the  cortex.  The  lymph  from  the  lymph  spaces  in  the 
medulla  enters  .the  plexus  and  from  this  the  lymph  of  the  cortex  and 
that  of  the  medula  is  carried  by  efferent  channels  through  the  hilus 
to  near  lymph  nodes.  The  lymph  of  part  of  the  cortex  and  the 
capsule  is  carried  by  efferents  from  the  capsular  plexus  to  neighbor- 
ing nodes. 

The  nerves  are  sympathetic  and  are  derived  from  the  solar  and 
renal  plexuses,  but  some  possibly  come  from  the  phrenic  and  vagal 
nerves  also.  These  nerves  form  a  plexus  in  the  capsule  and  from 
this  fibers  are  sent  to  the  cortex  and  others  to  the  medulla.  The 
latter  form  a  plexus  in  the  medulla.  The  cortical  fibers  are  for  the 
blood-vessel  around  which  they  form  plexuses.  In  the  medulla 
numerous  ganglion  cells  and  ganglia  are  seen.  The  fibers  of  this 
plexus  supply  the  vessels  here  as  well  as  the  epithelium.  The  fibers 
to  the  latter  terminate  upon  and  between  the  cells  in  little  knobs 
or  fine  fibrils. 


CHAPTER  XIII 
THE  MALE  GENITAL  SYSTEM 

The  male  generative  organs  form  a  very  complex  system.  They 
comprise  the  testes,  epididymi,  vasa  deferentia,  seminal  vesicles, 
ejaculatory  ducts,  prostate,  glands  of  Cowper  and  the  penis. 

In  the  human  being  and  in  most  mammals  the  testes  lie  outside 
of  the  body  in  a  sac-like  structure  called  the  scrotum.  This  con- 
sists of  a  number  of  layers.  Externally  it  is  covered  by  the  skin 
that  consists  of  stratified  squamous  cells  resting  upon  a  basement 
membrane  and  papillated  derma.  The  skin  is  darker  in  color 
than  in  common,  in  the  Caucasian,  due  to  the  presence  of  pigment 
in  the  Malpighian  layer.  It  contains  numerous  sweat  and  seb- 
aceous glands,  the  latter  being  connected  with  the  crisp  curly  hairs 
that  are  present.  The  skin  is  thrown  into  rugous  folds  and  in  the 
midline  there  is  a  ridge-like  elevation  that  is  continuous  with  a  like 
ridge  upon  the  under  surface  of  the  penis  and  the  skin  of  the  perineum. 
This  is  the  raphe  and  indicates  the  line  of  union  of  the  fetal  genital 
folds.  Beneath  the  skin  is  the  dartos  fascia.  This  consists  of  fibro- 
elastic  tissue  containing  a  considerable  quantity  of  smooth  muscle 
tissue.  The  elastic  tissue  is  abundant  as  is  also  the  muscle  tissue. 
This  dartos  forms  the  septum  that  divides  the  scrotum  into  two  sep- 
arate compartments.  The  muscle  tissue  is  peculiar  in  that  it  does 
not  respond  to  electrical  stimuli  as  ordinary  smooth  muscle  does. 
Cold,  or  extreme  warmth,  causes  it  to  contract  causing  the  scrotum 
to  become  shorter  and  thicker;  moderate  warmth  causes  the  muscle 
tissue  to  relax  and  the  scrotum  becomes  elongated  and  thinner  and 
that  portion  between  the  level  of  the  testes  and  the  attachment 
to  the  body  is  drawn  out  into  a  neck-like  part.  The  left  testicle 
is  usually  a  little  more  dependent  than  the  right.  Internal  to  the 
dartos  fascia  are  three  other  layers  of  fascia  composed  of  white 
fibrous  tissue  and  containing  some  voluntary  striated  muscle,  the 

35i 


352 


PRACTICAL   HISTOLOGY 


Cremaster  muscle.  These  are  derived  from  the  abdominal  wall 
during  the  formation  of  the  scrotum  and  the  descent  of  the  testes. 
Each  compartment  is  lined  by  a  serous  membrane,  the  parietal 
layer  of  the  tunica  vaginalis  testis,  that  is  derived  from  the  perito- 
neum. This  consists  of  a  single  layer  of  endothelial  cells  resting 
upon  the  fibro-elastic  subendothelial  connective  tissue.  It  is  con- 
tinuous with  the  serous  membrane,  visceral  layer,  that  invests  each 
testis.  Between  these  two  layers  is  a  serous  space  in  which  the 
testis  moves. 


Coils  of  vas 
deferens 

Vasa  efferentia 


Globus  major 


Cavity  of  tunica 

vaginalis 


Epididymis 


Mediastinum 

Parietal  layer  of 
tunica  vaginalis 


Tunica  albuginea 
Septa  of  gland 


Seminiferous 

tubules 


Septum 


Fig.  203. — Cross-section  of  Human  Testis  and  Epididymis,     (Eberth.) 

The  testis  is  another  compound  tubular  gland.  It  is  surrounded 
by  an  unusually  thick  capsule  called  the  tunica  albuginea,  which  is 
composed  of  bundles  of  white  fibrous  tissue  that  interlace  so  as  to 
form  a  very  tough  and  prominent  covering.  It  holds  the  substance 
of  the  testis  under  pressure  for  if  the  capsule  be  nicked  the  para- 
chyma  bulge  out  through  the  incision.  From  its  inner  surface,  pro- 
longations, or  trabecidce,  pass  into  the  center  of  the  organ  to  divide 
it  irregularly  into  compartments.  These  trabecular  all  converge  at 
the  dorsal  portion  of  the  organ,  where  the  capsule  is  very  thick, 
forming,  at  this  point,  a  thickened  mass  called  the  corpus  Highmori 


THE   URINARY   SYSTEM 


353 


or  mediastinum  testis.     Here  a  number  of  tubules,  to  be  described 
later,  are  found. 

The  compartments  correspond  to  the  lobules  of  other  glands^and 
the  septa  to  the  interlobular  connective  tissue  that  forms  a  complete 
wall  around  each  lobule.  In  the  lobules  is  the  interstitial  connective 
tissue  that  consists  of  a  delicate  network  of  loose  areolar  tissue. 


Globus  major 


Rete  testis 

Body  of 
epididymis 


Vasi  recti 


Va  i  deferens 


Fig.  204. — Longitudinal  Section  of  Human  Testis  and  Epididymis. 

{After  Bohm  and  Davidoff.) 


The  meshes  are  large  because  the  contained  seminiferous  tubules 
are  unusually  large.  The  elastic  tissue  is  abundant  and  many  fibers 
encircle  the  tubules  forming  a  part  of  their  tunica  propria.  This 
interstitial  tissue  supports  the  tubule,  blood-vessels,  nerves  and  some 
cells  called  the  interstitial  cells  of  Leydig.  These  are  scattered  or 
arranged  in  small  groups  and  in  some  animals  they  are  very  numerous 
forming  large  masses,  or  are  arranged  in  anastomosing  chains.  They 
are  large,  polyhedral  elements  the  coarsely  granular  cytoplasm  of 
23 


354  PRACTICAL  HISTOLOGY 

which  contains  crystalloids  and  fat  globules  and  a  double  centrosome. 
Elongated,  prismatic  crystals  have  also  been  found  but  their  origin 
and  nature  are  as  yet  unknown.  The  crystalloids  are  said  to  be 
mitochondria.  The  fat  reacts  readily  to  osmic  acid.  The  nucleus 
stains  well,  is  eccentrically  placed  and  contains  a  nucleolus.  These 
cells  are  said  to  be  derived  from  the  flattened  interstitial  connective- 
tissue  cells  by  a  direct  modification  of  these.  These  cells  are  fairly 
numerous  in  the  sexually  active  male  but  their  number  is  also  sub- 
ject to  individual  variation.  In  those  testes  that  are  not  actively 
functional  these  cells  are  more  numerous  and  usually  contain  more  fat. 

The  interstitial  cells  are  most  numerous  in  the  fetus,  diminish  in 
early  childhood  and  increase  again  at  puberty  and  are  fairly  numer- 
ous during  the  sexual  life  of  the  individual.  These  cells  manufacture 
an  internal  secretion  that  seems  to  control  sexual  impulses  and 
secondary  sexual  characteristics.  In  transplantation  experiments 
by  Steinach,  the  transplanted  ovaries  or  testes  showed  degenerative 
changes  in  the  ovarian  follicles  or  seminiferous  tubules  but  the  inter- 
stitial cells  were  increased  in  number.  Secondary  sexual  character- 
istics were  developed.  In  animals  that  have  regular  " seasons" 
these  cells  are  most  prominent  at  the  periods  of  sexual  activity. 
In  hybrids  that  are  incapable  of  reproducing  the  testes  contain 
great  numbers  of  interstitial  cells  and  the  sex  cells  are  poorly  de- 
veloped and  show  degeneration  signs.  Such  animals,  although 
incapable  of  reproduction,  experience  "heat." 

The  mediastinum  testis  occupies  about  one-third  of  the  dorsal 
border  of  the  organ.  It  consists  of  the  septa  that  comes  from  the 
capsule,  after  forming  the  compartments;  the  bundles  of  fibers 
form  a  coarse  meshwork  in  which  is  supported  the  blood-vessels, 
lymph  channels,  nerves  and  the  anastomosing  ducts  that  form  the 
excretory  ducts.  It  corresponds  to  the  hilus  as  it  is  here  that  the 
vessels  and  ducts  enter  or  leave. 

The  tunica  vaginalis  testis  is  a  serous  membrane  that  at  one  time, 
was  continuous  with  the  peritoneum.  It  covers  almost  the  entire 
organ,  and  is  attached  to  the  tunica  albuginea,  and  constitutes  the 
visceral  layer  of  the  tunica  vaginalis.  It  is  reflected  over  the  inner 
surface  of  the  scrotum  as  the  parietal  layer.  Some  writers  consider 
this  membrane  part  of  the  tunica  albuginea,  and  describe  it  as  such, 


THE   MALE    GENITAL    SYSTEM 


355 


but  as  it  is  genetically  (liferent,  it  should  be  considered  a  separate 
covering. 

The  parenchyma  of  the  testicle  is  made  up  of  tubules,  which, 
like  those  of  the  kidney,  are  very  convoluted,  and  consist  of  secretory 
and  conductive  portions.  These  tubules  are  the  seminiferous 
tubules,  and  are  collected  into  groups  which  correspond  to  lobules 
that  number  from  ioo  to  150. 


Fig.  205. — Human  Testicle. 
A,  Peripheral  portion  of  the  testicle  showing  the  capsule  and  tubules — a,  Tunica 
albuginea;  b,  blood-vessel;  c,  membrana  propria  of  tubule;  d,  interstitial 
cells;  e,  spermiogenetic  cells;  /,  lumen  of  longitudinal  tubule.  B,  Single 
seminiferous  tubule  highly  magnified — a,  Tunica  propria;  b,  basement 
membrane;  c,  spermiogonia;  d,  cells  of  Sertoli;  e,  mother  and  daughter 
cells;  /,  spermids;  g,  spermia.  C,  Spermia  highly  magnified.  D,  Tubule 
of  the  epididymis. 

The  seminiferous  tubules  are  said  to  end  blindly  underneath  the 
capsule  at  the  base  of  the  compartment  although  Bremer  states  that 
they  may  anastomose  or  branch. 

In  rabbits  the  two  tubules  of  a  lobule  are  continuous  like  a  U,  or 
one  limb  may  be  in  one  lobule  and  the  other  in  a  neighboring  lobule; 
again  the  anastomoses  may  be  more  complex.     These  anastomoses, 


356  PRACTICAL  HISTOLOGY 

according  to  Curtis,  are  most  numerous  in  the  rabbit,  less  so  in  the 
dog  and  uncommon  in  the  mouse.  There  are  said  to  be  three  to 
four  convoluted  tubules  in  each  compartment,  or  about  600  in  the 
testicle  of  man.  According  to  Lauth  there  are  800  to  900  semi- 
niferous tubules  in  each  testis. 

When  straightened  each  measures  about  50  to  80  cm.  in  length; 
the  length  of  them  all  together  is  given  as  650  to  800  meters.  At 
the  apex  of  a  compartment  these  convoluted  tubules  unite  to  form  a 
smaller  number  of  straight  tubules  that  are  conductive  in  function. 
These  are  the  vasi  recti,  which  pass  into  the  mediastinum,  where 
they  anastomose  to  form  a  network  called  the  rete  testis.  In  the 
upper  portion  of  the  mediastinum,  these  tubules  join  to  form  a  few, 
ten  to  fifteen,  vessels  that  pass  toward  the  edge*of  the  corpus  High- 
mori  as  the  vasa  efferentia.  As  these  leave  the  testicle,  they  be- 
come convoluted  and  dilated  into  cone-shaped  structures  called  the 
coni  vasculosa  or  globus  major,  of  the  epididymis.  The  coni 
vasculosa  unite  to  form  a  single  tubule  that  runs  a  very  convoluted 
course,  forming  a  narrow  continuation  of  the  above,  called  the  body 
of  the  epididymis.  At  the  the  lower  pole  of  the  testicle,  the  mass 
formed  by  the  continuation  of  the  body  is  somewhat  larger,  and  is 
named  the  globus  minor.  The  tubule  that  continues  from  this  point 
into  the  abdomen  is  called  the  vas  deferens. 

The  seminiferous  tubules  are  from  140  to  200  microns  in  di- 
ameter, and  form  the  bulk  of  the  testicle.  The  square  surface  of 
each  tubule  is  said  to  be  1784  sq.  mm.  Each  consists  of  a  small 
amount  of  tunica  propria,  and  a  basement  membrane,  upon  which  are 
found  two  to  three  layers  of  cells.  The  basement  membrane  is  thin 
and  delicate  and  rests  upon  the  relatively  thick  tunic  propria.  This 
measures  about  7  to  10  microns  in  thickness  and  consists  of  lamellae; 
the  inner  ones  are  closely  arranged  and  the  outer  ones  are  looser 
forming  a  meshwork  in  which  most  of  the  fibers  have  a  circular 
direction.  The  elastic  tissue  of  the  intertubular  region  contributes 
numerous  fibers  to  this  network.  The  cells  of  the  tunica  propria  are 
flattened  elements.  The  basal  layer  of  the  epithelial  cells  in  the 
tubules  consists  of  two  varieties,  the  spermiogonia,  which  are  the 
more  numerous,  and  the  sustentacular  cells,  or  columns  of  Sertoli. 
These  cells  vary  according  to  the  secretory  activity  of  the  organ. 


THE   MALE    GENITAL   SYSTEM  357 

Before  puberty  the  basal  cells  are  regular  while  the  other  cells  are 
polyhedral  and  practically  fill  the  tubule,  occluding  the  lumen. 
Some  spermiogonia  are  noted.  After  puberty  the  various  tubules  are 
not  all  in  the  same  stages  of  spermiogenesis.  In  those  tubules  in 
which  spermia  are  fully  developed  three  layers  of  cells  are  seen; 
(a)  basal  cells;  (b)  large,  clear  spermiocytes  derived  from  the  basal 
cells  and  these  spermiocytes  increase  by  their  own  mitosis;  (c)  sper- 
mids, smaller  cells  that  become  spermia.  The  spermids  are  derived 
from  the  spermiocytes  by  mitosis. 

The  basal  cells  comprise  the  spermiogonia  and  the  cells  of  Sertoli. 
The  spermiogia  are  fairly  large  cells  but  usually  not  so  large  as  the 
spermiocytes.  They  form  a  single  layer  along  the  basement  mem- 
brane with  the  Sertoli  cells  at  frequent  intervals.  The  cytoplasm  is 
finely  granular  and  stains  lightly.  The  nucleus  is  large,  stains 
deeply  and  mitotic  figures  are  numerous.  These  cells  by  mitosis 
give  rise  to  two  cells  one  of  which  remains  as  a  basal  cell  and  the 
other  one  becomes  a  spermiocyte  of  the  second  layer. 

The  sustentacula^  cells,  or  cells  of  Sertoli  are  seen  at  fairly  regular 
intervals  along  the  basement  membrane  and  their  appearance  varies 
with  the  stage  of  secretory  activity  of  the  tubule.  In  the  resting 
stage  each  is  a  rather  tall  pyramidal  cell  with  the  base  resting  upon 
the  basement  membrane.  The  cytoplasm  contains  pigment,  crys- 
talloids, lipoid  granules  and  fat  droplets.  The  origin  and  function  of 
the 'Crystalloids  is  as  yet  unknown.  The  nucleus  is  located  in  the 
basal  portion  of  the  cells,  contains  little  chromatin  but  presents  sev- 
eral chromatic  nuclei.  As  these  cells  apparently  nourish  the  sper- 
mids during  their  transformation  into  spermia  they  have  been  called 
trophocyles.  They  reproduce  by  the  direct  method.  In  the  stage 
of  secretory  activity  these  cells  increase  in  size  and  extend  through 
the  thickness  of  the  epithelial  layer  of  the  tubule.  At  that  time 
from  four  to  eight  spermids  become  attached  to  one  cell  and  as  their 
transformation  continues  these  spermids  become  inbedded  in  the 
cytoplasm  of  the  sustentacular  cell.  This  mass  of  cells  is  then  called 
a  spermioblast. 

The  spermatozoon,  or  spermium,  consists  of  three  main  parts, 
head,  middle-piece,  and  tail,  and  measures  52  to  62  microns  in 
length  (Krause). 


358  PRACTICAL  HISTOLOGY 

The  head  is  somewhat  pear-shaped  when  viewed  from  the  side  and 
is  4  to  5  microns  long  and  2  to  3  microns  wide  and  1  to  2  microns 
thick.  It  consists  of  the  condensed  chromatin  of  the  spermid  con- 
stituting n  or  12  chromosomes.  It  is  surrounded  by  a  delicate 
layer  of  protoplasm,  the  envelop,  or  galea  capitis.  In  some  mammals 
a  little  body  is  seen  at  the  front  part  of  the  head  just  beneath  the 
enveloping  protoplasm;  this  is  iheacrosome  {perforatorium)  and  it  rep- 
resents the  attraction  sphere  of  a  centrosome.  This  end  of  the  sper- 
mium  represents,  apparently,  a  cutting  edge,  and  in  some  lower  forms 
it  possesses  a  spiral  or  barbed  projection  that  assists  in  the  entrance 
of  the  spermium  into  the  ovum. 

The  middle-piece,  or  connecting  piece,  is  composed  of  several 
portions,  the  end-knob,  axial  fiber,  spiral  fiber  and  envelop.  The 
end-knob  connects  the  head  with  the  middle-piece  and  is  also  called 
the  neck.  Here  is  seen  the  divided  centrosome,  one  part  of  which 
becomes  a  flattened  mass  at  the  junction  of  head  and  middle-piece; 
the  other  elongates  into  the  axial  fiber  with  its  front  end  enlarged  to 
a  disc-like  mass  that  ultimately  separates  from  the  axial  fiber  to 
surround  it  as  a  darkly  staining  ring.  Surrounding  the  axial  fiber 
is  a  delicate  spiral  filament  that  is  probably  derived  from  the  mito- 
chondria. This  filament  is  not  distinct  in  the  spermia  of  man.  The 
envelop  is  a  thin  layer  of  protoplasm  that  surrounds  the  middle- 
piece  and  is  continued  over  the  head  and  tail  portions  of  the  spermium. 

The  tail  consists  of  axial  fiber  and  envelop.  The  axial  fiber  is  the 
continuation  of  the  axial  fiber  of  the  middle-piece,  but  is  not  so  promi- 
nent. It  represents  an  elongated  centrosome.  It  forms  the  motor 
portion  of  the  organism  and  its  origin  from  a  centrosome  is  not 
difficult  to  understand  when  we  consider  that  in  ameboid,  flagel- 
lated and  ciliated  cells  the  centrosome  presides  over  the  property  of 
motion.  It  is  about  5  microns  longer  than  the  envelop.  The  envelop 
represents  a  thin  protoplasmic  covering  of  the  axial  fiber  and  is 
continuous  with  that  of  the  middle-piece.  The  tail  is  about  41  to 
52  microns  long  and  about  1  micron  in  diameter. 

Abnormal  forms  of  spermia  are  found  such  as  double-tailed,  split- 
tailed,  four-tailed,  double-headed,  giant  and  dwarf.  These  defective 
spermia  are  thought  to  be  due  to  a  general  weakening  of  the  body 
from  illness,  alcohol,  drugs  and  coffee. 


THE   MALE   GENITAL   SYSTEM 


359 


Spermiogenesis  is  that  peculiar  change  by  which  spermia  are 
formed  from  cells  several  generations  removed  from  the  spermio- 
gonia,  or  original  cells.  The  male  somatic  cell  is  said  to  contain 
twenty-three  chromosomes. 

The  spermiogonia  represent  the  primordial  cells.  They  reproduce 
rapidly,  one  of  each  of  the  daughter  cells  remains  at  the  basement 
membrane  to  continue  the  cells  and  the  other  one  is  crowded  with 


C  E  F 

Fig.  206. — Diagram  of  the  Development  of  Spermia. 
(Stohr  after  Meves.) 

a.c,    Anterior  centrosome;   a.f.,   axial  filament;   c.p.,  middle  piece;  ch.p.,  tail; 
n,  nucleus;  nk,  neck;  p,  protoplasm;  p.c,  posterior  centrosome. 

the  cells  from  other  spermiogonia  to  form  the  other  layers  of  the 
tubule.  These  latter  cells  are  the  spermiocytes.  A  period  or  rest 
and  growth  intervenes  and  the  spermiocytes  increase  in  size  until 
they  are  quite  a  bit  larger  than  the  spermiogonia.  Then  maturation 
occurs.  These  primary  spermiocytes  prepare  for  mitotic  division 
but  instead  of  twenty-three  chromosomes  (diploid  number)  forming 
only  twelve  are  formed.  This  is  said  to  be  due  to  the  fusion  by 
pairs  of  the  original  twenty-three  and  the  twelve  constitute  the 


360  PRACTICAL  HISTOLOGY 

haploid  number.  One  of  the  twelve  is  a  single  chromosome,  it  having 
no  mate  in  the  fusion.  In  some  animals  the  double  form  is  apparent 
after  the  fusion.  In  the  formation  of  the  equatorial  plate,  or  mon- 
aster, eleven  of  these  chromosome  split  longitudinally  and  the 
unmated  chromosome  remains  whole.  This  is  the  X  Chromosome. 
When  the  cytoplasm  divides  eleven  of  these  daughter  chromosomes 
pass  into  one  daughter  cell  and  the  other  eleven  and  the  undivided 
(X)  chromosome  pass  into  the  other  daughter  cell.     These  secondary 

spermiocytes  are  about  one-half  the  size  of 
the  primary  spermiocyte  and  do  not  rest  and 
grow  to  any  extent  but  soon  divide.     As  each 
daughter  cell  divides  all  of  the  chromosomes 
split  longitudinally  (including  the  X  chromo- 
some) so  that  the  nuclear  spindle  of  one-half 
of  these  daughter  cells  contains  twenty-two 
daughter  chromosomes  and  the  other  half  of 
Fig  207  —Spermia        tne  daughter  cells  contain  twenty-four  daughter 
i,  2,  3,  Human  spermia:   chromosomes.     When  the  cytoplasmic  division 
i,  Surface  view;  2,  side   js  complete  the  four  granddaughter  cells,  or 

view;  3,  looped  seminal  .* 

filament.  4,  Spermium   spertmds,  are  ot  two  classes;  two  possess  eteven 
of  a  bullock:  a,  Head;   chromosomes  and  two  possess  twelve  chromo- 

b,  middle  piece;  c,  tail.  _      ,  ...  . 

somes.  Each  spermid  becomes  a  spermium, 
or  spermatozoon  and  if  one  containing  eleven  chromosomes  fertilizes 
an  ovum  the  offspring  will  be  a  male.  If  one  containing  twelve 
chromosomes  fertilizes  an  ovum  the  offspring  will  be  a  female. 
The  extra  chromosome  is  the  sex  determinant. 

In  the  formation  of  spermia,  the  spermids  are  of  the  most  impor- 
tance. According  to  some  authors,  the  nucleus  forms  the  whole 
organism,  while  others  hold  the  head  and  middle-piece  are  of  nuclear 
origin,  and  the  tail  protoplasmic.  These  cells  become  crowded  or 
drawn  to  the  columns  of  Sertoli,  to  which  they  apparently  attach 
themselves.  At  the  same  time,  the  shape  of  the  cell  becomes  modified 
by  elongation.  The  chromatin  of  the  nucleus  becomes  denser  and 
migrates  toward  the  attached,  or  peripheral  end,  while  the  protoplasm 
draws  toward  the  central  end.  At  the  attached,  or  peripheral  end, 
the  nucleus  has  a  small  prominence  developed  that  indicates  the 
future  head.     The  protoplasm  becomes  clear  and  draws  centrally, 


THE   MALE    GENITAL   SYSTEM 


361 


forming  a  slender  vesicle,  in  the  middle  of  which  a  delicate  line 
appears.  This  line  joins  the  head,  and,  growing  backward,  breaks 
through  the  cytoplasmic  membrane  to  form  the  tail  of  the  spermium. 
The  centrosomes,  usually  two  in  number,  become  different  in 
shape;  the  attraction  sphere  of  the  smaller  passes  to  the  head  of  the 
spermium  to  become  the  acrosome.  The  smaller  centrosome  then 
becomes  disc-shaped  and  attaches  itself  to  head  at  its  junction  with 
the  middle-piece;  the  larger  is  cone-shaped,  and  differentiates  into  two 


spc     spg 


spc    S  sptf       spc"      spg     spt 


Fig.  208. — Diagram  of  the  Process  of  Spermiogenesis  in  A  Longitudinal 
Section  of  a  Seminiferous  Tubule. 

sp,  spermia;  5,  cell  of  Sertoli;  spg,  spermiogonia;  spg',  same  in  mitosis; 
spc,  spermiocytes;  spc',  same  in  mitosis;  spt,  spermids;  spt",  spermiocytes 
changing  to  spermia.     (Sobotta.) 

portions,  the  larger  of  which  passes  toward  the  nucleus  (head),  and 
develops  a  flattened  extremity  just  behind  the  preceding  centrosome; 
the  remainder  elongates  into  the  axial  fiber  of  the  middle-piece  and 
tail.     The  envelop  is  held  to  be  cytoplasmic  in  origin. 

As  the  spermia  continue  to  develop,  the  column  of  Sertoli  increases 
in  length,  and  when  development  is  complete,  the  organisms  lie  in 
the  lumen  of  the  tubule.  The  column  of  Sertoli,  with  the  attached 
spermids,  is  called  a  spermioblast.  Loisel  believes  that  these  col- 
umns secrete  a  substance  that  attracts  the  spermids  (positive 
chemotaxis) . 

The  semen  consists  principally  of  spermia  suspended  in  a  fluid 
derived  from  the  various  portions  of  the  genital  tract.  It  is  a 
viscid,  whitish,  opalescent  fluid  of  an  alkaline  reaction  and  charac- 


362 


PRACTICAL  HISTOLOGY 


teristic  odor.  According  to  Lode  each  cubic  millimeter  of  semen 
contains  60,800  spermia;  an  entire  ejaculate  of  about  337c  cu.  mm. 
contains  about  200,000,000  spermia.  During  life  it  is  stated  that 
about  340  billions  are  formed  or  about  850  million  for  each  ovum. 
The  spermia  are  practically  amotile  until  mixed  with  the  secretion  of 
the  prostate,  when  they  become  actively  motile.  Beside  the  pros- 
tatic fluid  other  secretion  is  added  by  the  seminal  vesicles,  glands  of 


Spermatogonia 


Primary  Spermatocyte 


12    )  Secondary  Spermatocytes 


^j>  w 


Spermatids 


Spermatozoa 


Fig.  209. — Diagram  of  the  Cell  Divisions  in  Spermatogenesis. 

The  figures  indicate  the  number  of  chromosomes  found  in  the  cells  of  certain 

grasshoppers.     (Lewis  and  Stohr.) 


Cowper  and  urethral  glands  (Littre).  In  addition  to  the  spermia, 
crystals  and  amyloid  bodies  from  the  prostate,  fat  globules  and  epi- 
thelial cells  are  seen  in  the  semen. 

Motility  may  be  exhibited  by  the  spermia  twenty-four  hours 
after  death.  They  have  been  kept  alive  for  two  weeks,  under 
proper  conditions,  and  this  may  readily  occur  in  the  female  genital 
tract.  Water,  acids  and  metallic  salts  cause  cessation  of  action, 
while  alkaline  and  normal  salt  solutions  aid  it.  Batelli,  in  1902, 
found  by  experiments  that  the  spermia  travel  better  against^than 
with  the  current  although  Lott  (1872)  and  Hensen  (1876)  stated 
that  they  swim  against  the  current.     The  movement  depends  upon 


THE   MALE    GENITAL   SYSTEM  363 

the  strength  of  the  current.  The  spermia  move  at  the  rate  of 
about  60  microns  per  second. 

Motile  spermia  have  been  found  in  the  testicle  three  days  after 
execution.  They  have  been  found  in  the  vagina  twelve  to  seven- 
teen days  after  copulation  (Bassi)  while  Duhrsen  and  Zweifel  have 
found  living  spermia  in  diseased  oviducts  four  and  one-half  weeks 
after  coition.  In  one  to  two  hours  after  coition  the  spermia  are 
in  the  oviduct. 

The  excretory  system  starts  with  the  tubuli  recti.  These  lie  in 
the  apices  of  the  compartments  and  each  is  the  direct  continuation 
of  the  convoluted  seminiferous  tubules  but  is  much  smaller  in  di- 
ameter. Each  is  lined  with  simple  squamous  epithelial  cells  that  rest 
upon  a  basement  membrane  that  is  supported  by  a  delicate  tunica  pro- 
pria that  is  continuous  with  the  interstitial  tissue  of  the  lobule. 
Each  is  about  25  to  50  microns  in  diameter  and  passes  out  of  the 
lobule  to  form  the  next  part  of  the  excretory  system.  They  are 
the  same  in  number  as  the  seminiferous  tubules. 

The  rete  testis  is  made  up  of  the  anastomosing  tubuli  recti  and 
lies  in  the  mediastinum  testis.  These  tubules  have  a  larger  and 
more  irregular  diameter  than  the  foregoing  tubules  and  are  lined 
with  simple  squamous,  or  cuboidal  cells  that  rest  upon  a  basement 
membrane  and  tunica  propria. 

Along  the  dorsal  and  upper  part  of  the  mediastinum  the  tubules 
of  the  reti  testi  unite  to  form  ten  to  fifteen  tubules  that  constitute 
the  vasa  efferentia,  or  ductuli  efiferentes.  They  are  about  0.5 
mm.  in  diameter.  The  lining  cells  are  peculiar  in  that  in  some  areas 
it  is  simple  ciliated  and  in  others  nonciliated.  The  ciliated  cells 
are  low  and  the  cytoplasm  contains  fine  granules  that  are  acidophilic 
in  reaction.  The  nucleus  is  basally  placed.  The  nonciliated  cells 
are  columnar  or  polyhedral  cells  that  are  usually  collected  into 
groups.  The  cytoplasm  is  clear  and  the  nucleus  stains  well.  They 
seem  to  represent  secreting  cells  of  some  sort.  Beneath  the  basement 
membrane  is  a  tunica  propria  containing  a  considerable  quantity  of 
circularly  arranged  smooth  muscle  tissue. 

The  epididymis  consists  of  a  mass  of  convoluted  tubules  that 
lies  outside  of  the  testicle.  It  is  divided  into  three  portions,  the 
globus  major,  or  head,  the  body,  and  the  globus  minor  or  tail.    The 


364  PRACTICAL   HISTOLOGY 

globus  major  consists  of  ten  to  fifteen  large,  cone-shaped  tubules 
that  are  very  convoluted.  These  tubules  are  the  continuations  of 
the  vasa  efferentia.  The  cilia  are  the  largest  in  the  body.  The 
body  and  tail  consist  of  a  single  long  tubule  that  is  very  convoluted; 
if  straightened  it  would  measure  19  to  20  feet  in  length. 

The  epididymis  is  surrounded  by  a  dense  sheath,  or  capsule  of 
white  fibrous  tissue  that  divides  it  into  compartments.  In  the  globus 
major,  the  tubules  in  a  compartment  represent  the  convolutions  of 
one  of  the  coni  vasculosa. 

The  tubules  are  lined  by  statified  ciliated  cells  that  rest  upon  a 
basement  membrane,  outside  of  which  is  a  distinct  tunica  propria. 
The  ciliated  cells  of  the  coni  vasculosi  and  upper  part  of  the  body 
of  the  epididymis  are  said  to  be  true  ciliated  cells  while  the  remainder 
are  said  not  to  be.  In  these  latter  cells  the  protoplasmic  processes 
of  the  cilia,  within  the  cytoplasm  of  the  cell,  all  converge  to  one  point 
and  do  not  have  the  basal  particles.  In  the  true  cilia  cells  the  in- 
tracellular portion  of  each  cilium  is  separate  and  distinct  and  where* 
it  ends  in  the  cytoplasm  it  has  two  little  bodies,  called  basal  particles, 
attached  to  it.  These  particles  are  probably  of  centrosomic  origin. 
External  to  this  are  two  layers  of  smooth  muscle  tissue,  one  cir- 
cularly, and  the  other  (thin)  longitudinally  arranged. 

The  arteries  pass  into  the  mediastinum  and  divide  into  branches 
some  of  which  pass  into  the  interstitial  tissue  of  the  lobules  and  form 
plexuses  of  capillaries  around  the  tubules  and  others  pass  in  the  septa 
to  the  inner  surface  of  the  capsule  which  they  supply.  The  arteries 
are  thin-walled.  The  blood  is  collected  by  the  venules  that  have  a 
corresponding  course  and  carry  the  blood  from  the  compartments 
to  the  mediastinum  and  the  spermatic  cord.  Here  the  veins  branch 
and  anastomose  freely  forming  the  pampiniform  plexus  0}  veins  from 
which  one  vein,  the  spermatic,  carries  the  blood  into  the  abdominal 
cavity.  The  epididymis  receives  branches  from  the  spermatic 
artery  as  it  passes  into  the  mediastinum.  The  capillaries  ramify 
the  organ  and  the  venous  channels  return  the  blood  to  the  pam- 
piniform plexus. 

The  lympathic  vessels  form  plexuses  under  the  tunica  vaginalis, 
under  the  tunica  albuginea  and  in  the  interstitial  tissue  of  the 
lobules.     The  efferents  from  the  first  two  plexuses  follow  the  vessels 


THE   MALE   GENITAL   SYSTEM  365 

in  the  septa  to  the  mediastinum  and  join  the  efferent  from  the 
lobules.  The  lymph  spaces  in  the  lobules  pass  the  lymph  to  large 
sinus-like  channels  in  the  interstitial  tissue  and  the  efferents  carry 
the  lymph  to  the  mediastinum.  Here  all  of  the  efferents  follow  the 
veins  to  the  spermatic  cord  and  along  this  to  the  iliac  nodes  of  the 
abdominal  cavity. 

The  nerves  are  of  the  sympathetic  type  and  follow  the  blood-vessels 
which  they  supply.  Other  branches  are  said  to  enter  the  lobules 
and  end  in  relation  with  the  epithelial  cells.  The  branches  that 
supply  the  epididymis  may  have  ganglia  connected  with  them. 

THE  VAS  DEFERENS 

The  vas  deferens  connects  the  testicle  with  the  urethra.  It  passes 
into  the  body  through  the  inguinal  canal,  and  is  accompanied,  to  the 
internal  ring,  by  the  spermatic  artery  and  vein,  the  deferential 
artery,  pampiniform  plexus  of  veins,  cremaster  muscle  and  fibrous 
connective  tissue.  These  form  the  spermatic  cord.  At  the  internal 
ring  the  vas  continues  by  itself  to  the  under  surface  of  the  bladder 
and  near  its  termination  is  considerably  dilated;  this  part  is  called 
the  ampulla. 

The  vas,  or  ductus  deferens,  consists  of  three  coats, mucous, muscle 
and  fibrous. 

The  mucous  coat  consists  of  epithelial  cells,  basement  membrane 
and  tunica  propria.  The  epithelial  cells  of  the  first  part  are  of  the 
stratified  ciliated  variety  a  continuation  of  those  lining  the  epi- 
didymis. The  remaining  portion  is  lined  with  stratified  columnar 
cells.  The  basement  membrane  is  thin  and  rests  upon  the  areolar 
tunica  propria.  The  mucosa  is  thrown  into  longitudinal  folds  which 
are  larger  and  more  numerous  in  the  ampulla. 

The  muscle  coat  consists  of  three  layers  of  smooth  muscle  fibers, 
inner  longitudinal,  middle  circular  and  outer  longitudinal.  This  is 
usually  a  thick  coat  and  at  times  the  circular  muscle  fibers  are  not 
well  disposed  but  run  obliquely  and. interlace  with  the  bundles  of 
the  other  layers. 

The  fibrous  coat  consists  of  a  thin  layer  of  white  fibrous  tissue 
that  covers  the  muscle  coat  and  sends  in  fibers  between  the  muscle 
bundles. 


366 


PRACTICAL   HISTOLOGY 


The  vas  is  about  45  cm.  in  length  but  the  first  15  cm.  are  con- 
voluted or  coiled  into  a  small  mass  at  the  end  of  the  epididymis. 
The  remainder  runs  practically  a  straight  course.  The  diameter  is 
2  to  3  mm.  and  the  lumen  in  general  is  small.  The  diameter  of  the 
ampulla  is  6  to  8  mm.  and  the  lumen  is  proportionately  large. 

THE  SEMINAL  VESICLES 

The  seminal  vesicles  lie  beneath  the  bladder,  and  empty  into  the 
vas  through  the  seminal  ducts.  They  consist  of  three  coats,  mucous, 
muscular  and  fibrous. 


Fig.  210. — Section  of  the  Human  Seminal  Vesicle. 
(Photograph.     Obj.  16  mm.,  oc.  5  X-) 

The  epithelial  cells  are  of  the  simple  columnar  variety  though 
pseudostratified  cells,  or  two  layers  of  elements  may  be  seen.  The 
cytoplasm  of  these  cells  usually  contains  a  considerable  quanity  of 
yellowish  pigment  granules  that  are  characteristic  for  this  organ. 
These  are  probably  secretory  granules  and  with  the  desquamated 
cells  constitute  a  part  of  the  secretion  of  the  organ.  These  cells 
rest  upon  a  thin  basement  membrane  that  lies  upon  the  fibro-elastic 


THE   MALE   GENITAL   SYSTEM  367 

tunica  propria.  The  mucosa  is  thrown  into  a  great  many  folds  or 
rugae  that  run  in  all  directions  connecting  with  one  another  so  that 
sections  of  the  organ  sometimes  have  a  honeycomb  appearance. 
Small  areas  of  the  mucosa  may  give  the  appearance  of  enclosed 
glands. 

The  muscle  coat  consists  of  smooth  muscle  fibers  arranged  as 
inner  circular  and  outer  longitudinal  layers.  The  entire  coat  is 
said  to  be  thinner  than  the  corresponding  coat  of  the  vas. 

The  fibrous  coat  is  a  thin  layer  of  white  fibrous  tissue  and  besides 
supporting  the  muscle  coat  it  bridges  over  the  gaps  between  the 
coils  of  the  seminal  vesicle.  These  organs  act  as  reservoirs  for 
spermia,  at  times,  besides  secreting  a  fluid  that  helps  to  make  up 
the  semen. 

The  ejaculatory  duct  is  really  the  continuation  of  the  vas  but 
apparently  is  formed  by  the  junction  of  the  vas  and  the  duct  from 
the  seminal  vesicle.  It  has  a  thinner  wall  than  the  seminal  vesicle 
and  is  about  18  mm.  in  length.  It  passes  through  the  substance 
of  the  prostate  gland  and  opens  into  the  urethra  in  the  urethral  crest. 
It  consists  of  three  coats. 

The  mucous  coat  consists  of  simple  columnar  cells  that  rest  upon  a 
basement  membrane  and  tunica  propria.  The  latter  is  thrown  into 
folds  so  that  the  mucosa  has  an  irregular  appearance.  The  muscle 
coat  consists  of  smooth  muscle  tissue,  chiefly  longitudinally  arranged 
and  is  thin.  In  the  prostate  this  muscle  blends  with  that  of  the 
prostatic  trabecular  At  the  urethral  extremity  the  lining  cells  are 
of  the  transitional  variety. 

THE  PROSTATE  GLAND 

The  prostate  is  a  pyramidal  organ  that  is  situated  so  that  the 
middle  of  its  base  is  opposite  the  urethral  orifice  of  the  bladder;  as  a 
result  the  urethra  traverses  the  prostate  from  base  to  apex.  It  is 
pierced  on  each  side  by  the  ejaculatory  ducts  as  they  pass  through 
the  organ  to  the  urethral  crest.  Some  call  it  a  branched  tubular 
and  others  a  compound  tubuloalveolar  gland.  It  really  consists  of 
thirty  to  fifty  little  branched  tubular  glands,  sometimes  referred  to 
as  lobules.     The  organ  is  surrounded  by  a  thin  layer  of  white  fibrous 


368  PRACTICAL  HISTOLOGY 

connective  tissue  beneath  which  is  the  true  capsule  that  consists  of 
smooth  muscle  tissue.  This  forms  a  very  thick  layer  and  from  its 
deep  surface  tapering  trabecular  of  smooth  muscle  pass  toward  the 
urethra  and  divide  the  prostate  into  compartments  in  which  are 
the  glands.  These  trabecular  contain  also  some  white  fibrous  tissue 
which  continues  into  the  lubules  and  forms  a  reticulum  for  the 


&%5$  ;:v,p- 


i  •      -     :  ft  -^f^^'^sj 


s 

Fig.  211. — Section  of  the  Prostate  Gland. 

a,  Interstitial  tissue  and  muscular  trabecula;   b,  capsule;  c,  glands;  d,  amyloid 

bodies;  e,  secretion;/,  blood-vessel;  g,  duct. 

support  of  the  gland  tubules  and  the  vessels  and  nerves.  The 
smooth  muscle  tissue  is  not  found  around  the  tubules.  The  central 
ends,  of  the  trabecular  blend  with  the  muscle  tissue  of  the  urethra. 
The  trabecular  form  about  thirty  to  fifty  lobules  that  represent  the 
number  of  glands.  The  smooth  muscle  tissue  of  the  intertubular 
stroma  may  be  in  the  form  of  isolated  fibers  or  small  bundles. 
Connective-tissue  cells  are  numerous. 


THE   MALE    GENITAL   SYSTEM 


369 


The  glands  arc  distributed  chiefly  lateral  and  dorsal  to  the  urethra 
in  the  form  of  a  short  deep  crescent,  on  cross-section.  The  open 
dorsal  portion  is  filled  in  with  smooth  muscle  tissue.  Each  gland 
is  a  branched  tubular  or  tubuloalveolar  structure  and  consists  of  the 
secreting  tubules  and  a  short  duct. 

The  secreting  tubules  are  lined  with  a  single  layer  of  columnar 
elements,  although  some  state  that  in  places  several  layers  may  be 
present.  The  finely  granular  cytoplasm  contains  some  yellowish 
granules.     The  deeply  staining  nucleus  is  basally  placed.     These 


Fig.  212. — Section  of  the  Human  Prostate  Gland. 
(Photograph.     Obj.   16  ram.,  oc.  7.  5    X.) 

cells  rest  upon  a  basement  membrane  and  outside  of  this  is  the  areolar 
tunica^  propria  which  is .  composed  of  white  fibrous  tissue.  The 
tubules  usually  have  a  large  diameter  and  the  lumen  is  large.  The 
mucosa  is  thrown  into  folds  that  may  be  extensive  and  high,  in 
places  extending  all  of  the  way  across  the  lumen  and  dividing  the 
tubule  into  two  areas.  The  size  of  the  tubules  and  the  number  of 
folds  vary  in  different  animals.  In  the  lumina  of  many  of  the 
tubules  peculiar  masses,  circular  in  outline  are  seen.  These  are  the 
amyloid  bodies,  or  prostatic  concretions;  they  vary  in  size  from  a  few 
microns  to  a  millimeter  in  diameter.  These  are  fewer  and  smaller 
in  the  young  and  increase  in  number  and  size  as  age  advances.     The 

24 


370  PRACTICAL  HISTOLOGY 

ducts  are  twelve  to  fifteen  in  number  on  each  side.  These  are 
comparatively  short  and  each  opens  individually  in  the  urethra  in  a 
groove  at  each  side  of  the  urethral  crest  called  a  prostatic  sinus. 
These  have  been  described  in  the  male  urethra.  The  proximal  ends 
of  the  ducts  are  lined  with  simple  columnar  cells  but  the  distal 
extremities  are  lined  with  transitional  cells  continued  in  from  the 
prostatic  portion  of  the  urethra. 

The  secretion  of  the  prostate  gland  is  a  viscid,  opalescent  fluid 
that  is  acid  in  reaction.  In  man  the  spermia,  before  they  reach  the 
urethra,  are  amotile  or  only  feebly  so  but  when  mixed  wTith  the  pro- 
static fluid  they  become  actively  motile.  In  some  animals  as  the 
white  rat  and  guinea-pig  the  prostatic  fluid  is  passed  into  the  vagina 
of  the  female  after  the  semen  has  been  passed  and  then  it  coagulates 
and  forms  a  plug  that  prevents  the  escape  of  the  semen.  Atrophy 
of  the  prostate  occurs  after  the  removal  of  the  testes  and  in  old 
individuals  the  organ  is  subject  to  hypertrophy. 

The  arteries  enter  the  organ  through  the  capsule  and  branches 
follow  the  trabeculae  and  enter  the  lobules  and  form  extensive 
capillary  plexuses  around  the  tubules  and  in  the  trabeculae  for  the 
supply  of  the  abundant  muscle  tissue.  The  blood  is  collected 
by  venous  channels  that  run  toward  the  periphery  and  form  a  network 
in  the  capsule. 

The  lymphatics  originate  in  the  septa  and  follow  the  venous 
channels. 

The  nerves  are  mainly  sympathetic.  They  enter  the  capsule  and 
here  numerous  small  ganglia  may  be  seen.  Some  of  the  nerve  supply 
the  muscle  tissue  and  other  sympathetic  fibers  apparently  end 
between  the  epithelial  cells.  The  myelinated  fibers  terminate  in 
corpuscles  that  resemble  those  of  Krause. 

The  glands  of  Cowper,  or  bulbourethral  glands  are  racemose  glands 
that  empty  into  the  penile  portion  of  the  urethra.  They  are  sur- 
rounded by  a  capsule  of  white  fibrous  tissue  that  divides  the  gland 
into  lobes  and  lobules.  The  interlobular  septa  contain  both  smooth 
and  voluntary  straited  muscle  fibers.  The  alveoli  that  make  up  a 
lobule  are  fined  by  low  columnar  mucous  cells.  Some  of  these  cells, 
however,  contain  fine  granules  that  are  acidophilic  in  reaction  and 
do  not  respond  to  the  mucin  stains.     These  rest  upon  a  cellular 


THE    MALE    GENITAL   SYSTEM  37 1 

basement  membrane  and  tunica  propria.  The  smaller  ducts  are 
lined  by  cuboid al  cells,  while  the  larger  possess  stratified  columnar 
cells.  The  muscle  coat  of  the  main  duct  consists  of  longitudinally 
arranged  smooth  muscle. 

The  main  duct  of  each  gland  passes  through  the  superficial  layer 
of  the  triangular  ligament  and  empties  into  the  bulbous  portion  of 
the  urethra. 

THE  PENIS 

The  penis  is  an  organ  surrounded  by  a  loosely  attached  skin.  The 
latter  contains  no  adipose  tissue.  The  thin  skin  extends  over  the 
end  of  the  organ  as  the  prepuce,  which  is  covered,  upon  both  sur- 
faces, by  stratified  squamous  cells.  The  inner  surface  possesses  the 
characteristics  of  a  mucous  membrane. 

The  organ  consists  of  two  main  portions,  the  glans  and  the  body. 

The  glans  is  covered  by  stratified  squamous  cells,  and  is  separated 
from  the  body  by  a  narrow  constricted  area,  the  cervix.  At  this 
point,  the  squamous  cells  of  prepuce  and  glans  are  continuous. 

The  body  consists  of  two  corpora  cavernosa  and  the  single  corpus 
spongiosum. 

The  corpora  cavernosa  lie  side  by  side,  forming  the  dorsal  portion 
of  the  penis,  and  are  bound  together  by  a  thick  sheath  of  white 
fibrous  tissue  called  the  tunica  albuginea.  From  the  inner  surface 
of  this,  trabeculce  pass  inward  and  form  a  series  of  communicating 
spaces,  or  caverns.  These  are  venous  blood  spaces.  The  trabecular 
contain  tortuous  arteries,  the  helicine  arteries,  which,  when  engorged, 
become  straightened  as  the  organ  increases  in  size.  The  spaces 
become  filled  with  blood,  and,  with  the  vascular  trabecular,  con- 
stitute true  erectile  tissue.  This  engorgement  produces  the  erection. 
False  erectile  tissue  depends  for  its  action  upon  smooth  muscle  tissue. 

The  corpus  spongiosum  has  a  thin  tunic,  and  consists  of  two  por- 
tions, urethral  and  peripheral.  The  urethral  part  is  quite  dense  and 
rich  in  veins,  while  the  peripheral  part  resembles,  somewhat,  the 
cavernous  portion. 

The  glans  is  a  continuation  of  the  corpus  spongiosum,  and  consists 
of  a  delicate  network  of  connective  tissue  enclosing  a  number  of 
small  spaces.     It  is  covered  by  a  delicate  skin,  which  is  continuous 


372 


PRACTICAL  HISTOLOGY 


with  the  prepuce,  or  foreskin.  In  the  cervix  are  located  a  number  of 
glands  that  secrete  the  smegma.  These  are  the  glandules,  oderiferce. 
The  blood-vessels  and  spaces  are  numerous.  The  arterial  branches 
follow  the  septa,  in  which  they  run  such  a  convoluted  course  as  to 
receive  the  name  of  helicine  arteries.  They  form  capillary  plexuses 
in  the  trabecular,  some  of  which  empty  into  .the  spaces,  while  others 
pass  over  into  the  veins.  The  branches  within  the  tunica  form 
capillaries  that  empty  into  the  spaces.  Anastomoses  between  arte- 
rial and  venous  capillaries  are  numerous. 


Fig.  213. — Cross-section  of  the  Penis  of  an  Adult. 

a, a,    Corpora  cavernosa;     b,  corpus  spongiosum  with  the  urethra;     c,  tunica 
albuginea.     (Photograph.     Obj.  72  mm.) 


The  emissary  veins  receive  blood  from  the  tunica  and  superficial 
vessels,  and  partly  from  the  deeper  tissues  and  vessels;  they  pass 
through  the  tunica  to^empty  into  the  dorsal  vein  of  the  penis  that 
lies  in  a  groove  between  the  corpora  cavernosa.  These  veins  are 
pressed  upon  when  the  superficial  vessels  are  filled  with  blood,  in  that 
way  preventing  egress,  but  not  ingress,  of  the  blood. 

The  lymphatics  of  the  penis  are  abundant.  Plexuses  exist  in  the 
subcutaneous  tissue  of  the  body  and  glans,  in  the  prepuce  and  in 
the  mucosa  of  the  urethra.     The  efferents  conduct  the  lymph  to  the 


THE    MALE   GENITAL   SYSTEM  373 

superficial  inguinal  nodes.  The  deeper  lymph  vessels  of  the  skin 
and  of  the  trabecular  form  a  plexus  and  the  efferents  conduct  the 
lymph  along  the  blood-vessels  to  the  iliac  nodes. 

The  nerves  are  both  cerebrospinal  and  sympathetic.  The  cere- 
brospinal are  both  motor  and  sensor;  the  motor  supply  the  ischiocav- 
ernosus  muscles  and  the  sensor  terminate  in  various  ways.  The 
free  endings  are  among  the  epithelial  cells  of  the  glans  and  urethral 
mucosa.  In  the  papillae  of  the  skin  are  tactile  corpuscles  (Meissner's) ; 
deeper  in  the  derma  are  corpuscles  of  Krause  and  in  the  skin  of  the 
glands  are  the  genital  corpuscles;  in  the  connective  tissue  of  the 
corpora  cavernosa  Pacinian  bodies  are  seen.  The  sympathetic 
fibers  supply  the  musculature  of  the  vessels  and  also  the  smooth 
muscle  in  the  trabecular.  Vasodilatator  nerves  to  the  vessels  are 
derived  from  the  third  and  fourth  sacral  nerves  (through  the  sym- 
pathetics)  and  these  are  the  nervi  erigentes. 

The  paradidymis,  or  organ  of  Giraldes,  is  found  in  the  epididymis. 
It  consists  of  a  number  of  tubules,  in  which  the  lining  cells  are  low 
columnar  or  even  ciliated.  The  tubules  are  closed,  and  are  separated 
from  one  another  by  vascular  connective  tissue. 

The  cells  that  line  the  various  portions-  of  the  male  genital  tract 
are  as  follows: 

Testicle. 

Spermiogonia      ]Basall 

Sustentacular 

Spermiocytes,  or  mother  cells. 

Second  layer. 
Daughter  cells,  Third  layer. 
Spermids,  Fourth  layer. 

Tubuli  Recti Cuboidal  or  squamous. 

Rete  Testis Cuboidal  or  squamous. 

Vasa  Efferentia Columnar  or  ciliated. 

Epididymis Stratified  ciliated. 

_.     _   ,  |  Stratified  columnar. 

' ' ' '  [  Stratified  ciliated  (some). 
Seminal  Vesicles .% Simple  or  pseudostratified  col- 
umnar. 
Ejaculatory  Duct Simple  columnar. 


Seminiferous  Tubule. 


CHAPTER  XIV 
THE  FEMALE  GENITAL  SYSTEM 

This  system  consists  of  the  ovaries,  oviducts,  uterus,  vagina, 
glands  of  Bartholin  and  genitalia. 

The  ovary,  the  distinctive  female  organ,  is  attached  to  the  dorsal 
surface  of  the  broad  ligament  and  lies  in  the  fossa  ovarica  at  the  side 
of  the  pelvic  cavity.  It  is  3.75  cm.  long,  18  mm.  wide  and  8  mm. 
thick.  It  is  surrounded  by  a  capsule  of  white  fibrous  connective 
tissue  called  the  tunica  albuginea.  This  is  not  so  prominent  as 
that  of  the  testicle.  The  free  surface  of  the  capsule  is  covered  by 
low  columnar  cells  called  the  geminal  epithelium. 

The  organ  consists  of  cortex  and  medulla.    1 


Fig.  214. — A  Human  Ovary. 
a.   White     line;  b,   mesovarium;   C,   oviduct.     (After  ftagel.) 

The  cortex  is  the  outer  part,  and  surrounds  the  medulla,  except 
at  one  point,  at  which  the  vessels  enter  and  leave;  this  is  the  hilum, 
and  here  the  medulla  comes  to  the  surface.  The  cortex  is  the  glandu- 
lar portion,  where  the  cellular  elements  of  the  secretion,  the  ova, 
are    formed.     It    consists    of  a  delicate  reticulum,  the  stroma,  in 

374 


THE    FEMALE    GENITAL   SYSTEM  375 

which  the  Graafian  follicles,  corpora  lutea  in  various  stages,  and  oc- 
casionally groups  of  large,  polygonal  epithelial  cells,  called  the  inter- 
stitial cells  are  found.  The  free  surface  of  the  stroma  is  covered 
by  the  modified  mcsothelial  cells,  the  germinal  epithelium,  from  which 
the  ova  are  derived.  These  cells  are  low  columnar  elements  and  not 
peritoneal  endothelial  cells. 

The  Graafian  follicles  are  characteristic  structures.  They  vary 
in  size;  the  smallest  are  just  beneath  the  tunica  albuginea,  the 
medium-sized  near  the  medulla,  and  the  largest  extend  from  the 
medulla  to  the  capsule,  and  cause  a  projection  upon  the  surface  of 
the  organ. 


Fig.  215. — A  Section  of  a  Human  Ovary. 
a,   Corpus    luteum;  b,   Graafian    follicles;   c,  corpus     albicans.      (After  Nagel  ) 

Externally  the  mature  follicle  is  covered  by  a  layer  of  condensed 
stroma  called  the  theca  folliculi;  the  outer  portion  of  this  is  called 
the  tunica  fibrosa,  and  the  inner  the  tunica  vasculosa.  The  theca 
is  lined  by  a  number  of  layers  of  granular  cells  termed  the  zona 
granulosa,  within  which  is  a  space,  the  antrum,  rilled  by  a  liquid, 
the  liquor  folliculi.  At  one  point,  the  granule  layer  projects  into 
the  antrum,  and  this  mass  contains  the  ovum.  This  projection  is 
called  the  discus  proligerus,  or  cumulus  ovigerus.  Just  within  the 
granule  cells  of  the  discus  is  seen  a  layer  of  long  columnar  cells, 
the  corona  radiata.  A  well-defined  corona  radiata  indicates  that  the 
maturity  of  the  ovum  is  almost  completed  (Bischoff,  Waldeyer). 
These  cells  rest  upon  a  thick  homogenous  membrane  called  the  zona 
pellucida,  which  is  separated  from  the  ovum  by  a  small  space,  called 
the  perivitelline  space.     This  space  is  disputed  by  some  writers. 


376 


PRACTICAL  HISTOLOGY 


The  corona  is  supposed  to  give  rise  to  the  zona  pellucida.  The  ovum 
that  lies  just  within  the  space  consists  of  a  cell-wall,  the  vitelline 
membrane,  and  cell-body,  the  vitellus.  In  the  vitellus  is  seen  the 
nucleus,  or  germinal  vesicle,  which  contains  the  prominent  nucleolus, 
or  germinal  spot. 


e  t£ 


Fig.  216. — Cross-section  of  Ovary  of  a  Cat. 

The  Graafian  follicles  are  so  numerous  that  but  little  of  the  medulla  is  seen. 
a.  Germinal  epithelium;  b,  tunica  albuginea;  c,  immature  Graafian  follicle; 
d,  ovum;  e,  cortical  stroma;  /,  interstitial  cells;  g,  theca  folliculi;  h,  zona 
granulosa;  *,  antrum  containing  liquor  folliculi;  k,  discus  proligerus;  I, 
corona  radiata;  m,  zona  pellucida;  n,  vitellus;  o,  germinal  vesicle;  p,  follicle 
without  ovum;  r,  hilum;  s,  medulla  showing  the  tubules  of  the  parovarium; 
t,  arteriole;  u,  venule. 


The  ovum  is  the  most  characteristic  and  largest  cell  in  the  female. 
Its  diameter  varies  from  0.22  to  0.32  mm.  The  zona  pellucida 
that  surrounds  it  is  quite  thick,  measuring  from  10  to  n  microns 
(Ebner).  It  is  probably  the  result  of  the  activity  of  the  cells 
of  the  follicle.  It  is  said  to  contain  small  radial  canals  called  micro- 
pyles,  through  which  the  spermlum  gains  entrance  to  the  ovum  in 
fertilization  (denied  by  Keibel  and  others).     The  cytoplasm  consists 


THE   FEMALE   GENITAL  SYSTEM  377 

of  a  delicate  reticulum  and  of  yolk  granules,  the  nutritive  yolk,  or 
deutoplasm,  and  the  formative  yolk,  and  is  transparent  in  all  stages. 
The  ooplasm  consists  of  two  layers,  an  outer  marginal  zone  that  is 
finely  granular  and  contains  the  germinal  vesicle,  the  central  portion 
contains    the   bulk   of    the    deutoplasm.     The   latter    consists    of 


y 


I 


v 


/•  \  | 


/ 


J 


■ 

7  -  v  -  » 

Fig.  217  — Ovum  of  a  Woman  Thirty  Years  of  Age.    (McMurrich.) 
cr,  Corona  radiata;  zp,  zona  pellucida;  p,  protoplasmic  zone  of  ovum;  ps,  peri- 
vitelline  space;  y,  yolk  (deutoplasm);  n,  nucleus  (germinal  vesicle)  showing 
germinal  spot. 

fine  and  coarse  granules  1  to  3  microns  in  diameter;  they  are  fatty 
in  nature.  The  cytoplasm  often  contains  chromidia  that  represent 
the  yolk  nucleus;  the  accessory  nuclei  may  be  independent  or  attached 
to  the  nucleus  and  may  be  also  basophilic  or  acidophilic  in  reaction. 
These  are  said  to  be  remnants  of  mitotic  spindles.  Mitochondria  are 
also  present.  The  nucleus  averages  about  30  to  50  microns,  is  ec- 
centrically placed  and  sharply  outlined  by  a  membrane  that  possesses 


373 


PRACTICAL  HISTOLOGY 


a  double  contour.  The  chromatin  is  rather  scant  in  the  matured 
ovum,  but  the  nucleolus  is  quite  large  (7  to  10  microns)  and  promi- 
nent. In  the  immature  ovum  the  chromatin  usually  forms  a  dense 
mass.  The  nucleolus  may  be  acidophilic,  basophilic  or  neutrophilic. 
The  centrosome  may  be  seen  in  ova  that  have  not  undergone  maturation. 
If  this  process  has  been  completed  the  centrosome  disappears.  Hertwig 
states  that  they  are  found  in  ova  of  rabbits  up  to  six  or  seven  weeks 
of  age,  and  in  young  guinea-pigs.  Multinuclear  ova  are  formed  by 
fusion  of  separate  ova  or  by  direct  division  of  the  nucleus  alone. 


Fig.  218. — Section  of  the  Ovary  of  a  Child  at  Birth  showing  Numerous 
Immature  Graafian  Follicles  and  one  Well  Developed.  In  the  Lat- 
ter the  Zona  Granulosa  has  shrunken  away  from  the  Follicu  li. 
(Photograph.     Obj.  16  mm.,  oc.     10  X). 

The  Graafian  follicles,  of  which  there  are  about  36,000  in  each 
ovary,  are  developed  during  intrauterine  life,  and  all  are  usually 
present  at  birth.  At  birth  or  shortly  after  all  oogonia  have  become 
mother  cells  (oocytes  of  the  first  order).  Not  all  of  these  develop, 
by  any  means.  Hensen  estimates  that  about  200  follicles  in  each 
ovary  mature.     The  other  follicles  enlarge  to  a  certain  stage  and 


THE   FEMALE   GENITAL   SYSTEM 


379 


then  undergo  atrophy  and  are  absorbed.  The  smallest  consist  of 
the  ovum,  surrounded  closely  by  a  few  layers  of  small  granule  cells 
and  a  delicate  theca.  They  lie  just  beneath  the  tunica  albuginea, 
and  show  no  antrum.  The  medium-sized  follicles  lie  near  the 
medulla,  and  present  an  antrum.  The  granule  cells  are  more 
numerous,  the  ovum  larger  and  the  corona  radiata  and  zona  pellucida 
appear.  The  fully  developed  follicles  extend  from  the  medulla 
through  the  cortex  beyond  the  original  surface  level,  projecting 
varying  distances. 

The  follicular  cells  are  derived  from  the  germinal  epithelium, 
and  grow  into  the  stroma  in  long  columns  during  the  developmental 


Odgonia 


Polar  Bodies 


Secondary  Oocyte 


Mature  Ovum 


Fig.  219. — Diagram  of  the  Cell  Divisions  in  Oogenesis.     (Compare  with 

Fig.  209.)     (Lewis  and  Stohr.) 


period,  as  the  egg-tubes  of  Pflueger.  In-  such  a  column  will  be 
found  several  large,  and  a  great  number  of  small  cells.  These 
columns  become  separated  into  a  number  of  groups  of  cells  consisting 
of  one  or  more  large,  and  many  small  cells.  The  large  are  the  oogen- 
etic, and  the  small  the  granule  cells.  Gradually,  the  large  cells  fuse 
to  form  a  single  mass  of  protoplasm,  and  all  the  nuclei,  except  one, 
disintegrate.  The  single  cell  resulting  is  called  the  oocyte.  The 
egg-tubes  are  separated  into  these  groups  by  the  stroma  that  grows 


380  PEACTICAL  HISTOLOGY 

into  the  columns.  This  stroma  further  condenses  around  each 
group  to  form  the  primitive  theca.  Toward  the  age  of  puberty, 
these  follicles  begin  to  develop,  though  they  may  start  sooner.  The 
granule  cells  increase  rapidly  in  number,  and  some  of  the  more  central 
ones  disappear  by  disintegration  or  liquefaction.  This  gives  rise 
to  the  space,  or  antrum,  which  becomes  rilled  by  a  liquid,  the  liquor 
folliculi.     The  latter  is  probably  derived  from  the  blood. 

Follicles  containing  several  ova  are  formed  as  follows:  (1)  The 
egg-tube  becomes  separated,  incompletely  enclosing  several  germ 
cells  in  one  mass;  (2)  fusion  of  two  originally  separated  follicles. 

Maturation  is  the  process  by  which  the  polar  bodies  are  formed 
and  extruded.  During  intrauterine  life  oogonia  multiply  rapidly 
as  do  the  spermatogonia  in  the  male,  but  the  latter  process  does  not 
occur  until  the  male  is  twelve  to  fifteen  years  of  age.  The  resulting 
oogonia  are  small  and  undergo  a  period  of  rest  and  then  growth  and 
are  then  called  primary  oocytes.  These  undergo  the  maturation 
process  which  is  the  same  as  in  the  spermiogonia.  The  germinal  ves- 
icle migrates  toward  the  periphery,  and  undergoes  mitotic  change. 
Only  twelve  chromosomes,  the  haploid  number,  are  formed  due  to 
fusion  by  pairs;  these  divide  longitudinally  forming  twenty-four. 
When  the  nuclear  spindle  is  formed  parallel  to  one  of  the  radii,  the 
peripheral  half,  surrounded  by  a  small  amount  of  cytoplasm,  is 
thrust  out  of  the  cell.  This  is  the  first  polar  body.  Without  rest, 
the  remaining  chromosomes  immediately  undergo  division  again, 
and  the  extrusion  process  is  repeated.  This  is  the  second  polar 
body.  The  remaining  chromosomes  form  a  new  nucleus  called  the 
germ-nucleus.  By  this  change,  the  number  of  chromosomes  is 
reduced  from  twenty-jour,  in  the  oogonium,  to  twelve,  in  the  matured 
ovum.  The  first  polar  body  often  divides  into  two,  and,  as  a  result 
of  maturation,  four  cells  are  formed.  Of  these  four,  the  ovum  is 
the  only  one  capable  of  producing  an  offspring.  The  three  polar 
bodies  disintegrate  and  disappear.  This  is  entirely  different  from 
the  change  in  the  testicle.  In  that  organ,  the  spermiocyte  gives 
rise  to  four  cells,  each  of  which  becomes  a  spermium,  capable  of 
fertilization. 

Maturation  of  the  ovum  differs  from  karyokinesis  in  the  following 
ways:  (1)  The  nucleus  moves  to  the  periphery  of  the  cell  instead  of 


THE   FEMALE   GENITAL   SYSTEM 


38l 


remaining  in  the  middle;  (2)  only  one-half  the  somatic  number  of 
chromosomes  is  formed;  (3)  the  resulting  daughter  cells  contain  only 
One-half  the  somatic  number  of  chromosomes;  (4)  the  resulting 
cells  are  unequal  in  size;  (5)  the  successive  divisions  occur  without 


Fig.  220. — Diagram    Illustrating    the    Reduction   of   the   Chromosomes 
during  the  Maturation  of  the  Ovum.     (McMurrich.) 
Ovum;  oc1,  oocyte  of  the  first  generation;  oc2,  oocyte  of  the  second  genera- 
tion; p,   polar  globule. 


rest;  (6)  the  mature  ovum  contains  no  centrosome;  (7)  only  one  cell 
is  of  functional  importance. 

The  differences  between  maturation  of  the  ovum  and  maturation 
of  the  spermiocyte  are  as  follows:  The  primary  oocyte  forms  four 


382  PRACTICAL  HISTOLOGY 

granddaughter  cells  of  which  only  one  is  nearly  as  large  as  the  pri- 
mary cells  and  the  other  three  are  very  small  immature  cells.  Al- 
though all  contain  the  same  number  of  chromosomes,  twelve,  only 
the  matured  ovum  is  of  functional  importance;  the  other  three  small 
cells,  or  polar  bodies  disintegrate  and  disappear.  As  the  spermiocyte 
undergoes  maturation  (spermio  genesis)  four  granddaughter  cells  are 
formed  but  these  are  all  small  and  of  the  same  size.  Two  contain 
only  eleven  chromosomes  and  two  contain  twelve  chromosomes.  All 
of  these  cells,  however,  are  of  functional  importance  as  any  one  is 
capable  of  fertilizing  a  matured  ovum. 

As  the  follicle  increases  in  size,  it  approaches  the  tunica  albuginea, 
and  causes  it  to  protrude.  The  stroma  intervening  between  the 
ovum  and  the  tunica  gradually  diminishes  until  merely  the  tunica 
albuginea  remains.  As  the  follicle  increases  and  the  pressure  within 
becomes  greater,  the  tunica  becomes  progressively  thinner,  until 
it  is  no  longer  able  to  withstand  the  pressure.  A  small  area,  the 
stigma,  is  the  thinnest  part  and  indicates  the  place  of  rupture. 
Then  it  ruptures,  and  the  liquor  folliculi  and  the  ovum,  surrounded 
by  the  granule  cells,  are  cast  out  of  the  ovary.  The  vessels  of  the 
tunica  vasculosa  rupture,  and  the  follicle  fills  with  blood.  When 
this  occurs,  the  body  is  called  the  corpus  hemorrhagicum.  The 
cells  of  the  theca  penetrate  the  clot,  and  cause  this  to  organize.  In 
addition  to  these  cells,  there  are  certain  other  large  cells  that  possess 
a  yellowish  pigment.  These  are  the  lutein  cells,  and  their  function 
is  unknown.  These  are  derived  from  the  theca.  These  increase 
in  number  and  make  a  very  large  body.  The  corpus  exhibits  a 
pleated  appearance  due  to  the  invagination  of  the  white  fibrous 
tissue  of  the  theca  folliculi  and  the  blood-vessels. 

If  the  ovum  has  not  been  fertilized,  this  body  is  called  a  corpus 
luteum  spurium,  which  rapidly  undergoes  atrophy.  In  a  few  weeks, 
it  leaves  a  white  scar  called  the  corpus  albicans,  due  to  the  increase 
of  radially  disposed  white  fibrous  tissue  and  its  resultant  contraction. 
If  fertilization  has  occurred,  then  the  body  persists  until  near  the 
end  of  pregnancy,  and  is  termed  the  corpus  luteum  verum. 

The  corpus  luteum  seems  to  be  a  gland  of  short  duration.  It 
seems  to  secrete  a  substance  that  causes  the  second  succeeding 
menstrual  flow,  that  is,  of  the  next  month.     Experimental  study 


THE   FEMALE    GENITAL    SYSTEM 


3%3 


upon  animals,  in  which  the  follicles  were  destroyed,  showed  an  almost 
invariable  absence  of  the  second  succeeding  period.  The  preceding 
flow  was  caused  by  the  follicle  preceding  the  experiment.  This 
secretion  also  stimulates  the  uterus,  and  aids  the  implantation  of  the 
ovum  in  the  uterine  mucosa,  providing  fertilization  has  occurred 
(Frankel).  During  pregnancy  it  seems  to  prevent  the  maturation  of 
Graafian  follicles,  while  during  the  later  stages  of  pregnancy  it  is 
said  to  exert  an  influence  upon  the  mammary  gland. 


Fig.  221. — Section  of  a  Corpus  Albicans  in  the  Cortex  of  the  Ovary  of  an 
Adult  Female.     (Photograph  Obj.  16  mm.,  oc.     7.5  x.) 

Of  all  the  follicles  formed,  but  few  are  ever  fertilized.  A  great 
number  atrophy;  in  the  remainder,  maturation  occurs.  Of  these 
ova,-  there  are  those  which  are  cast  into  the  abdominal  cavity  and 
absorbed  by  the  peritoneum;  those  which  pass  down  the  genital 
tract  and  are  cast  out,  or  disintegrate,  and  lastly,  those  that  become 
fertilized. 

Ovulation  includes  the  delivery  of  the  ovum  from  the  follicle 
and  its  passage  through  the  genital  apparatus.  In  the  lower  animals, 
in  which  the  young  are  developed  from  eggs  outside  of  the  body 
(oviparous),  this  process  is  evinced  by  the  "laying  of  the  egg." 
In  the  viviparous  animals,  or  those  in  which  the  offspring  is  developed 


384  PRACTICAL  HISTOLOGY 

within  the  mother,  this  process  is  not  accompanied  by  any  outward 
signs  or  manifestations.  In  the  temperate  climate,  it  begins  at 
about  the  twelfth  to  the  fifteenth  year,  and  continues  until  about 
the  forty-fifth  to  the  fiftieth  year.  At  this  time  ovulation  ceases, 
and  fertilization  cannot  occur  thereafter. 

The  medulla  consists  of  a  loose  network  formed  by  large,  coarse 
bundles  of  white  fibrous  tissue,  in  which  strands  of  smooth  muscle 
tissue  are  found.  These  latter  are  limited  to  the  medulla.  In  the 
meshes  of  the  stroma  are  seen  the  interstitial  cells,  which  are  more 
numerous  than  in  the  cortex.  The  interstitial  cells  resemble  those 
of  the  testis.  Some  believe  them  to  be  the  remains  of  some  of  the 
cells  of  the  fetal  genital  organs,  others  that  they  are  scattered 
germinal  epithelial  cells  that  are  considered  capable  of  developing 
into  ova;  still  others  consider  them  derivatives  of  the  connective- 
tissue  cells  and  not  embryonal  remains.  In  this  part  of  the  ovary 
are  found  the  large  blood-vessel  trunks  which  are  very  numerous. 

The  ovarian  and  uterine  arteries  supply  the  ovary.  These  vessels 
pass  into  the  hilus  of  the  ovary  between  the  layers  of  the  mesovarium 
forming  a  number  of  branches  that  enter  the  medulla.  These 
branches  are  comparatively  large  and  have  a  spiral  course  resembling 
the  helicine  arteries  of  the  male.  Their  walls  are  unusually  thick, 
due  to  the  presence  of  an  excessive  amount  of  smooth  muscles  a 
great  deal  of  which  is  longitudinally  arranged.  Branches  from 
these  pass  into  the  cortex  where  capillary  plexuses  are  formed 
in  and  around  the  theca  of  the  Graafian  follicles  and  others  form 
capillary  plexuses  in  the  stroma.  The  extent  of  the  plexuses  around 
the  follicles  depends  upon  the  state  of  the  follicle.  When  these 
are  young  and  immature  the  plexus  is  not  extensive;  as  the  follicles 
mature  the  plexus  becomes  greater  and  increases  until  after  the 
rupture  of  the  follicle  and  during  the  active  stage  of  the  corpus 
luteum.  As  this  retrogrades  the  capillary  plexus  becomes  reduced 
so  that  in  the  corpus  albicans  it  is  less  than  in  the  surrounding 
stroma.  The  blood  is  collected  by  venules  that  have  thin  walls; 
these  pass  to  the  medulla  where  they  form  the  pampiniform  plexus 
of  veins  analogous  to  that  of  the  male.  From  this  plexus  the  ovarian 
vein  carries  the  blood  from  the  organ. 

Lymph  spaces  are  numerous  and  they  pass  the  lymph  into  large 


THE   FEMALE    GENITAL    SYSTEM  385 

capillaries  that  accompany  the  blood-vessels.  These  capillaries 
form  plexuses  around  the  large  follicles  and  the  lymph  is  conducted 
by  efTerents  to  the  hilus  where  these  vessels  join  those  from  the  body 
of  the  uterus.  The  lymph  ultimately  reaches  the  pelvic  and  lumbar 
nodes. 

The  nerves  are  derived  from  the  ovarian  plexus  of  the  sympathetic 
system,  enter  the  hilus  and  are  distributed  to  the  smooth  muscle 
in  the  stroma,  the  smooth  muscle  of  the  vessels  and  some  fine 
fibrils  are  said  to  end  between  the  epithelial  cells  of  the  zona  granu- 
losa. Pacinian  bodies  are  also  described  as  being  present.  Wini- 
warter states  that  along  the  nerves  and  in  the  medulla  there  are 
small  ganglia  that  contain,  besides  the  ganglion  cells,  groups  of 
pheo chrome  cells. 

The  parovarium,  or  epoophoron,  lies  near  the  hilus  of  the  ovary, 
and  consists  of  a  number  of  short  vertical  tubules  united  to  a  single 
horizontal  tube.  The  vertical  tubules  are  short,  and  are  lined  by 
low  columnar  cells.  The  horizontal  tubule  has  a  larger  diameter 
than  the  preceding,  and  is  lined  by  the  same  variety  of  cells.  It 
often  lies  deep  in  the  broad  ligament. 

The  paroophoron  lies  in  the  broad  ligament,  between  the  ovary 
and  uterus,  and  consists  of  a  number  of  short,  closed  tubules  lined 
by  low  columnar  cells.  The  tubes  resemble  the  vertical  tubes  of 
the  epoophoron. 

THE  OVIDUCT 

Although  the  ovary  possesses  no  excretory  apparatus  like  other 
glands,  the  oviduct,  or  Fallopian  tube,  acts  as  such. 

The  oviduct  consists  of  the  outer  fimbriated  end,  the  middle,  or 
ampulla,  and  the  inner  uterine  end,  or  isthmus.  It  has  three  coats, 
mucous,  muscular  and  fibrous. 

The  mucous  coat  consists  of  simple  ciliated  cells  that  lie  upon  a 
basement  membrane  and  tunica  propria.  A  muscularis  mucosce  is 
absent.  The  cilia  wave  in  such  a  manner  as  to  create  a  current 
toward  the  uterus.  Here  and  there  are  seen  patches  of  nonciliated 
cells  but  none  of  the  glandular  nature  are  present.  The  basement 
membrane  is  thin  and  homogeneous.  The  fimbria  are  finger-like,  or 
fringe-like  projection  one  of  which  is  especially  large  and  is  attached 

25 


386 


PRACTICAL   HISTOLOGY 


to  the  ovary.  The  others  are  free.  Each  fimbrium  consists  of  a 
core  of  fibro-elastic  tunica  propria  covered,  on  the  lumen  side  by 
simple  ciliated  cells  and  upon  the  abdominal  cavity  side  by  the 
endothelial  cell  of  the  peritoneum,  though  at  times  the  ciliated 
cells  seem  to  surround  the  whole  structure.  The  tunica  propria 
is  thrown  into  longitudinal  folds  that  are  high  in  the  fimbriated  end, 
but  diminish  in  height  as  the  uterus  is  approached.  These  folds 
are  the  villi,  which  possess  a  very  narrow  base,  but  the  part  lying 


Fig.  222. — Cross-section  of  the  Human  Oviduct. 
a,  Epithelium;  b,  tunica  propria;  c,  villi;  d,  muscular  coat,  inner  circular  layer; 
e,  muscular  coat,  outer  longitudinal  layer;  /,  blood-vessels  in  the  fibrous 
coat;  g,  blood-vessels  in  villus;  h,   fibrous  coat;  k,  epithelium  of  fimbria; 
/,  tunica  propria  of  fimbria. 


in  the  lumen  of  the  tube  is  greatly  branched  forming  the  secondary 
folds.  The  tunica  propria  consists  of  white  fibrous  and  yellow 
elastic  tissues,  in  which  diffuse  lymphoid  tissue  is  found.  The 
mucosa  is  thickest  at  the  fimbriated  extremity  and  the  lumen  varies 
from  2  to  8  mm.  in  diameter  in  the  different  parts.  The  uterine 
extremity  has  the  smallest  lumen. 


THE   FEMALE   GENITAL   SYSTEM  387 

The  muscle  coat  consists  of  smooth  muscle  tissue.  This  is  ar- 
ranged into  inner  circular  and  outer  longitudinal  layers.  The  inner 
circular  layer  is  the  broader  and  some  of  its  fibers  are  oblique  in 
direction  and  may  penetrate  the  tunica  propria  of  the  mucosa. 
This  layer  is  thickest  at  the  uterine  extremity  of  the  oviduct.  The 
outer  longitudinal  layer  is  in  general  poorly  developed  and  in  areas 
may  be  wanting.  It  is  said  to  be  best  developed  opposite  to  the 
attachment  of  the  mesosalpinx.  It  is  thickest  at  the  fimbriated 
extremity  of  the  oviduct.  At  the  uterine  extremity  an  inner  longi- 
tudinal layer  is  added.  This  probably  represents  a  muscularis 
mucosae.  The  whole  muscle  coat  is  thickest  at  the  uterine  end 
of  the  tube. 

The  fibroserous  coat  consists  of  a  thin  layer  of  white  fibrous  tissue 
that  is  the  real  fibrous  coat.  This  is  invested  by  a  layer  of  the  peri- 
toneum which  is  derived  from  that  of  the  broad  ligament.  Opposite 
to  the  free  edge  of  the  tube  the  two  layers  of  the  peritoneum  unite 
and  form  a  delicate  band  that  connects  the  tube  to  the  broad  liga- 
ment; this  band  is  the  mesosalpinx.  Through  this  the  vessels,  nerves 
and  lymphatics  gain  access  to  or  leave  the  organ. 

The  arteries  are  branches  of  the  ovarian  and  uterine  arteries. 
These  pass  to  the  tube  between  the  layers  of  the  mesosalpinx  and 
at  the  fibrous  coat  send  branches  into  the  other  coats.  These  form 
capillaries  in  the  muscle  and  mucous  coats  and  the  blood  is  collected 
by  venules  that  form  a  plexus  in  the  muscle  coat  and  from  here  the 
blood  is  carried  by  larger  venules  that  accompany  the  arteries. 

The  plexus  of  lymph  vessels  in  the  mucosa  sends  the  lymph  to 
the  serous  coat,  as  is  also  the  case  of  the  plexus  in  the  muscle  coat. 
From  the  serous  coat  efferents  carry  the  lymph  to  pelvic  and  lumbar 
nodes. 

The  nerves  are  from  the  ovarian  sympathetic  plexus.  The 
branches  pass  to  the  muscle  tissue  of  the  tube  and  the  vessels  and 
other  fibers  form  a  subepithelial  plexus  from  which  probably  fine 
branches  pass  to  the  epithelial  cells  of  the  mucosa. 

THE  UTERUS 

The  uterus  is  a  flattened,  pear-shaped  organ  that  consists  of 
body  and  cervix.     It  is  an  important  organ,  as  within  it  develops 


388  PRACTICAL  HISTOLOGY 

the  offspring,  in  viviparous  animals.  It  is  about  7.5  cm.  long, 
5  cm.  wide  and  2.5  cm.  thick  in  the  virgin.  In  this  condition  it 
weighs  from  1  to  i}4  ounces.  After  the  first  pregnancy  it  never 
returns  to  this  weight  and  size.  All  parts  consist  of  mucous, 
muscular  and  fibrous  coats. 

The  mucous  coat  of  the  body  is  about  2  mm.  in  thickness  (Hitsch- 
mann  and  Adler)  of  a  grayish  color  and  smooth,  and  is  composed 
of  simple  ciliated  cells,  basement  membrane  and  tunica  propria. 
Mandle  (1908)  states  that  the  amount  of  ciliated  epithelium  varies. 
Within  the  tunica  propria  are  found  a  rich  capillary  plexus  and  diffuse 
lymphoid  tissue.  The  surface  is  not  smooth,  but  is  broken  by  the 
formation  of  glands.  These  are  tube-like  depressions,  lined  by  the 
simple  ciliated  cells,  of  the  branched  tubular  variety;  these  glands  are 
slightly  spiral,  in  course  obliquely  directed  and  usually  their  ends 
are  bent  upon  themselves.  They  are  the  uterine  glands  and  extend 
to  the  muscular  coat,  and  may  even  penetrate  the  inner  layer.  They 
are  often  so  long  that,  when  they  reach  the  muscular  coat,  they  turn 
and  extend  parallel  to  it  for  some  distance. 

The  tunica  propria  of  the  uterus  is  said  to  resemble  embryonic 
connective  tissue.  Elastic  fibers  are  said  to  be  absent  and  the  white 
fibers  are  present  in  small  numbers.  Cells  are  very  numerous, 
some  of  which  are  lymphocytes  and  these  constitute  diffuse  lymphoid 
tissue.  The  other  cells  are  oval,  or  spindle-shaped  and  may  have 
branches.  In  addition,  especially  during  the  formation  of  the  men- 
strual mucosa,  there  are  some  large  clear  cells  present  called  decidual 
cells.  These  are  also  found  in  the  placenta  and  are  no  doubt 
derived  from  the  uterus  during  the  formation  of  the  placenta. 

The  mucosa  of  the  cervix  is  a  little  different.  The  uterine  end 
is  lined  by  simple  ciliated  cells,  and  glands  are  present.  The  vaginal 
end  is  lined  by  stratified  squamous  cells,  and  gland-like  depressions  are 
present.  The  orifices  often  closed,  causing  them  to  become  distended 
with  secretion.  In  this  condition,  they  produce  globular  projections 
called  the  ovuli  Nabothi.  The  cervical  mucosa  is  thrown  into  folds 
called  the  plicae  palmatae.  The  vaginal  portion  of  the  cervix  is 
covered  by  stratified  squamous  cells. 

The  muscle  coat  of  the  body  of  the  uterus  is  arranged  in  layers  in 
some  animals  but  in  the  human  being  these  layers  are  not  distinct. 


[•HE    FEMALE    GENITAL   SYSTEM 


389 


In  the  cervix,  however,  they  are  distinct.  In  the  body  the  innermost 
layer  represents  a  greatly  hypertrophied  muscularis  mucosa  and  ac- 
cording to  Shafer  this  forms  the  greater  part  of  the  thickness  of 
the  wall  of  the  uterus.  In  the  fundus  the  bundles  of  fibers  form 
concentric  rings  around  the  openings  of  the  oviducts;  in  the  cervix 
and  lower  part  of  the  body  they  have  a  circular  direction  and  a  few 


Fig.  223. — Resting  Uterine  Mucosa. 
a.    Mucosa;  b,   epithelium;  c,   gland  tubule.      (Slbhr's  Histology,  after  Bbhm  and 

Davidoff. ) 

internal  longitudinal  fibers  may  be  present.  The  middle  portion 
consists  of  bundles  of  fibers  that  have  a  circular  direction  but  inter- 
lace somewhat.  The  main  blood-vessel  trunks  are  in  this  layer 
and  these  with  the  areolar  tissue  present  make  this  the  widest  layer 
of  the  organ.  The  presence  of  the  blood-vessels  makes  it  resemble  a 
submucosa  and  the  layer  is  called  the  stratum  vasculare.  There 
may  be  some  longitudinal  fibers  along  its  internal  part.      According 


39° 


PRACTICAL   HISTOLOGY 


to  Shafer  this  layer  is  best  developed  over  the  dorsal  and  lateral 
parts  of  the  fundus.  The  outermost  fibers  are  called  the  stratum 
supr avascular e.  The  fiber  bundles  are  chiefly  longitudinally  directed 
and  form  a  thin  layer  just  beneath  the  serous  coat.  Some  of  the 
bundles  are  continuous  with  those  of  the  oviducts,  the  round  liga- 
ments and  broad  ligaments.  The  innermost  fibers  of  this  layer 
have  a  circular  direction. 

In  the  cervix  the  muscle  fibers  are  arranged  into  distinct  layers, 
inner  and  outer  longitudinal  and  middle  circular.  The  circular  fibers 
form  the  sphincters  at  the  internal  os  and  external  os. 

The  muscle  fibers  average  50  to  60  microns  in  length;  but,  during 
pregnancy,  they  lengthen  to  from  300  to  600  microns. 

The  fibrous,  or  serous,  coat  is  quite  thin.  It  is  completely 
invested  by  peritoneum  in  the  body. 

Menstruation  is  the  periodic  change  that  occurs  in  the  uterine 
mucosa,  every  twenty-eight  days,  during  the  child-bearing  period 
(thirteenth  to  fiftieth  year).  The  superficial  part  of  the  mucosa 
softens,  disintegrates  and  is  removed.  It  is  divided  into  stages,  the 
premenstrual,  or  hypertrophic,  menstrual,  or  desquamative,  post- 
menstrual,  or  reparative  and  intermenstrual,  or  resting  stages. 

1.  The  premenstrual  stage  requires  usually  six  to  seven  days. 
The  mucosa  increases  two  to  three  times  in  thickness  due  to  edema 
and  enlargement  of  cellular  elements.  The  gland  lumina  become 
wider  and  irregular  due  to  the  projection  of  epithelium  and  tunica 
propria.  The  secretion  in  the  glands  is  mucous.  The  superficial 
connective  tissue  cells  become  larger,  rounded  and  the  cytoplasm 
becomes  clearer;  they  represent  preliminary  decidual  cells.  In  these 
changes  the  mucosa  becomes  divided  into  two  layers,  stratum  com- 
pactum  and  stratum  spongiosum.  The  vessels  dilate  and  become 
engorged  and  the  mucosa  is  of  a  deep  red  color.  "Hemorrhages 
occur  within  tunica  propria,  these  areas  become  confluent  forming 
a  subepithelial  hematoma. 

2.  The  menstrual  stage  shows  the  epithelial  denuded  at  intervals 
permitting  the  blood  to  flow  mixed  with  edematous  fluid  and  gland- 
ular secretion.  As  a  result  of  this  outflow  there  is  a  rapid  shrinkage 
in  the  thickness  of  the  mucosa.  The  glands  are  collapsed,  the 
lumina  straight  and  the  cells  smaller  and  lower.     The  decidual  cells 


THE    FEMALE    GENITAL    SYSTEM 


391 


degenerate,  disappear  or  diminish  in  size.  The  surface  epithelium 
may  be  only  slightly  affected  or  the  entire  stratum  compactum  may 
be  expelled.  This  stage  occupies  from  three  to  five  days  during 
which  time  26  to  52  cu.  cm.  of  blood  is  lost  according  to  Hoppe-Seyler. 


Disintegrating  'tT&fiBfr    £&&*.        ^\ 

epithelium         ^V'r^.W^vv^^w'fe    <$v^§Sc 

•Excretory  duct    "\£p v?v/ /V:^  AM,:Kv?M ^S"**"* If^sTN^""  " 


im/.'M  .> 


Dilated  tubule 


Blood  vessel —  -- 


Superficial 
epithelium 


Disintegrating 
epithelium 

Pit-like 
depression 


—  Excretory  duct 


Gland  tubule 


Blood  vessel 


Muscularis 


Fig.  224. — Mucous  Membrane  of  a  Virgin  Uterus  During  the  First  Day 
of  Menstruation.      X  30.     (Schaper.) 

3.  In  the  postmenstrual  stage  the  glands  are  narrow  and  straight, 
the  former  decidual  cells  are  long  and  fusiform  and  only  small 


392  PRACTICAL   HISTOLOGY 

hemorrhagic  areas  are  to  be  seen.  After  a  few  days  the  glands 
become  wavy,  the  lining  cells  enlarge  somewhat  and  the  mucosa 
becomes  quiescent.     This  stage  requires  from  four  to  six  days. 

4.  During  the  intermenstrual  stage  the  gland  cells,  at  first  small 
and  closely  set,  enlarge  and  the  cytoplasm  becomes  hemogeneous 
and  acidophilic.  In  the  tunica  propria  leukocytes  and  even  solitary 
nodules  are  seen.  The  gland  cells  produce  secretory  granules  that 
are  passed  into  the  gland  lumina.  This  stage  occupies  fourteen 
days.  Should  fertilization  occur  at  this  time  of  the  premenstrual 
stage,  the  other  three  stages  may  not  take  place.  Bryce  and  Teacher 
claim  that  menstruation  occurs  merely  to  maintain  a  mucosa  at  all 
times  ready  for  the  formation  of  a  decidua. 

The  uterus  of  the  female  at  birth  is  different  in  appearance  than 
at  the  age  of  puberty  and  in  the  adult  condition.  The  mucosa  is 
comparatively  thin  and  the  epithelial  runs  a  smooth  and  unbroken 
course  as  glands  are  not  present.  These  form  between  the  first 
and  fifth  years. 

The  blood-vessels  are  important.  Two  arteries,  the  uterine  and 
ovarian,  supply  the  organ.  The  main  branches  of  these  arteries 
pass  to  the  middle  circular  layer  of  muscle,  where  they  form  an 
extensive  plexus  of  large  vessels  as  in  the  submucosal  of  other  organs. 
From  this  plexus  branches  pass  to  the  muscle  coat  and  form  plexuses 
of  capillaries;  other  branches  pass  to  the  mucosa  and  form  a  dense 
capillary  meshwork  just  under  the  epithelium.  The  extent  of  this 
plexus  will  differ  at  the  various  stages  of  menstruation.  The  blood 
is  collected  by  venules  that  accompany  the  arterial  channels. 

Lymphatic  spaces  and  capillaries  are  numerous  in  the  mucosa.  The 
capillaries  form  an  extensive  meshwork  and  receive  the  lymph  from 
the  spaces.  The  lymph  is  carried  by  efferents  to  the  plexus  in  the 
inner  muscle  layer  and  then  to  another  in  the  muscular  coat  proper 
and  from  here,  by  means  of  valved  vessels,  the  lymph  is  conducted 
to  the  subserous  plexus,  ultimately  to  be  carried  to  the  neighboring 
lymph  nodes. 

The  nerves  are  from  the  cerebrospinal  and  sympathetic  systems 
through  the  pelvic  plexus.  These  supply  the  muscle  tissue  of  the 
uterus  and  of  the  vessels  from  a  plexus  formed  in  the  stratum 
vasculare;  other  fibers  from  this  plexus  are  said  to  form  a  delicate 


THE    FKMALE    GENITAL    SYSTEM 


393 


subepithelial  plexus  from  which  terminal  fibers  pass  between  the 
epithelial  cells  of  the  mucosa. 

THE  VAGINA 

The  coats  of  the  vagina  are  the  same  as  those  of  the  uterus. 
The  mucous  coat  consists  of  stratified  squamous  cells,  supported 
by  basement  membrane  and  tunica  propria.     The  subepithelial  portion 


Fig.  225. — Cross-section  of  Segment  of  Human  Vagina. 

a,  Stratified  squamous  epithelium;  b,   tunica  propria;  c,  inner  circular  muscle 

fibers;  d,  outer  mixed  muscle  fibers. 

of  the  tunica  propria  is  papillated.  The  deeper  portion  contains 
many  large  elastic  fibers  and  considerable  diffuse  lymphoid  tissue. 
Occasionally,  some  simple  tubular  glands  are  met  with,  and  the 
lining  cells  are  of  the  simple  ciliated  variety. 


394  PRACTICAL   HISTOLOGY 

The  muscular  coat  varies  in  thickness,  that  nearer  the  outlet  being 
the  thicker.  The  layers  are  not  sharply  separated  from  one  another, 
but  the  general  direction  is  inner  circular  and  outer  longitudinal. 
The  fibers  are  long  and  slender.  The  mucous  and  muscular  coats 
are  thrown  into  folds  that  are  called  rugae.  The  outlet  of  the  vagina 
is  surrounded  by  voluntary  striated  muscle  tissue  that  is  called  the 
sphincter  vagina  muscle. 

The  fibrous  coat  consists  of  dense  fibrous  tissue,  and  serves  to 
connect  the  vagina  with  the  surrounding  tissues  and  organs.  It 
contains  the  large  blood-vessels,  lymphatics  and  nerves. 

The  larger  vessels  lie  in  the  deeper  portion  of  the  fibrous  coat  and 
send  branches  into  the  mucosa  and  muscularis.  The  capillaries  of 
the  mucosa  pass  chiefly  to  the  papillae.  The  veins  form  dense 
plexuses  beneath  the  fibrous  coat.  Large  vessels  occur  in  the  deeper 
part  of  the  mucosa,  causing  it  to  resemble  cavernous  tissue. 

The   lymphatics  follow   the   same   course   as   the   blood-vessels. 

The  nerves  are  both  myelinated  and  amyelinated.  These  form  an 
extensive  plexus  containing  a  number  of  small  ganglia  in  the  fibrous 
coat;  from  this  plexus  motor  fibers  pass  to  the  muscle  tissue  of  the 
vessels  and  vaginal  wall  and  sensor  fibers  pass  to  the  epithelium  of 
the  mucosa. 

THE  GENITALIA 

The  vaginal  orifice  is  guarded  by  a  delicate  annular,  or  crescentic 
membrane  called  the  hymen.  This  consists  of  white  fibrous  tissue 
covered  upon  its  external  and  internal  surfaces  by  stratified  squamous 
cells.     Occasionally,  it  is  very  vascular. 

Just  outside  of  this  fold,  the  primitive  urinogenital  sinus  spreads  to 
form  the  vestibule  of  the  vagina.  This  is  a  triangular  space,  with 
the  apex  formed  by  the  junction  of  the  labia  minora,  the  sides  by 
these  folds  and  the  base  by  the  vaginal  orifice.  It  contains  the 
opening  of  the  urethra.  This  space  is  lined  by  stratified  squamous 
cells.  In  the  tunica  propria,  are  found  a  great  many  elastic  fibers 
and  mucous  and  sebaceous  glands,  especially  near  the  opening  of 
the  urethra.  The  lower  portion  of  the  tunica  propria  contains  so 
many  large  venous  channels  that  it  is  practically  erectile  tissue. 

Opening  into  the  vestibule  .upon  each  side  is  a  gland,  the  analog 


THE   FEMALE    GENITAL   SYSTEM  395 

of  the  gland  of  Cowper  of  the  male.  This  is  the  gland  of  Barthob'n, 
which  is  a  compound  racemose  fjjand,  and  the  acini  are  lined  by  large, 
clear,  mucous  cells.     The  ducts  are  lined  by  low  columnar  cells. 

Covering  the  vaginal  orifice,  to  a  greater  or  less  extent,  are  seen 
the  labia  minora,  or  nymphae.  These  consist  of  a  central  mass  of 
loose  connective  tissue,  in  which  the  blood-vessels  are  abundant, 
especially  the  veins.  In  the^  tissue  between  the  veins,  smooth 
muscle  tissue  exists,  and  this  with  the  vascularity,  forms  the  erectile 
tissue.  The  folds  are  covered  upon  both  sides  by  stratified  squamous 
cells  that  rest  upon  a  papillaled  tunica  propria.  In  these  papillae, 
capillary  plexuses  are  seen.  Sebaceous  glands  are  numerous,  but 
hairs  and  sweat-glands  are  absent. 

The  glans  clitoris  lies  in  the  tissue  formed  by  the  junction  of  the 
labia  minora.  It  is  covered  by  stratified  squamous  cells.  The 
central  part  consists  of  erectile  tissue,  and  many  large  and  small 
vascular  papillae  are  present.  Genital  corpuscles  and  sebaceous 
glands  are  found.  The  glans  is  covered  by  a  fold  of  skin,  the 
prepuce,  in  which  the  sebaceous  glands  are  quite  numerous. 

The  labia  majora  are  merely  folds,  or  pouches  of  skin.  Their 
outer  surfaces  are  covered  by  ordinary  skin.  In  the  subcutaneous 
tissue  are  seen  numerous  vessels,  nerves,  glands,  bundles  of  smooth 
muscle  and  an  abundance  of  adipose  tissue.  Along  the  median  line, 
they  come  in  contact  with  each  other,  and  the  skin  surface  is  some- 
what modified.  Here  elastic  and  muscle  tissue  are  abundant,  but 
adipose  tissue  is  wanting.  The  skin  of  the  labia  majora  is  somewhat 
darker  than  that  in  the  immediate  neighborhood,  due  to  the  pres- 
ence of  pigment  in  the  epithelial  layers.  Over  the  pubis,  the  two 
labia  meet  and  form  a  prominent  mass,  the  mons  veneris. 

The  various  portions  of  the  female  genital  tract  are  lined  by  the 
following  cells : 

Oviduct Simple  ciliated. 

Uterus. 

Body Simple  ciliated. 

Cervix  Uterine  end Simple  ciliated. 

Vaginal  end Stratified  squamous. 

Vagina Stratified  squamous. 

Vestibule Stratified  squamous. 

Labia Stratified  squamous. 


CHAPTER  XV 
THE  PLACENTA  AND  UMBILICAL  CORD 

A  description  of  the  formation  of  the  placenta  and  cord  must  be 
given  in  order  to  understand  their  structure  at  term. 

Should  the  ovum  become  fertilized,  it  is  passed  down  the  oviduct 
by  the  ciliated  cells,  as  fertilization  usually  occurs  in  this  portion  of 
the  genital  system.  It  is  surrounded  by  the  zona  pellucida  and 
corona,  or  zona  radiata.  The  mucous  membrane  of  the  uterus 
becomes  thickened,  as  for  menstruation,  and  the  ovum  becomes 
lodged,  usually  in  the  fundus.  The  implantation  process  requires 
about  one  day.  If  the  implantation  is  in  the  main  cavity  of 
the  uterus  it  is  called  central,  as  in  carnivors,  rabbits,  etc.;  if  in 
a  furrow  or  diverticulum  it  is  called  excentric,  as  in  hedge-hog  and 
mouse;  if  it  is  by  destruction  or  erosion  of  the  mucosa  and  there- 
fore outside  of  the  uterine  cavity  proper  in  the  interstitial  tissue 
it  is  called  interstitial,  as  in  man  and  guinea-pig. 

The  mucosa  of  the  uterus  is  divided  into  regions:  that  immediately 
beneath  the  ovum  is  the  placental  decidua.  or  decidua  basalis;the 
ovum  becomes  covered  by  a  portion  called  the  decidua  capsularis, 
or  ovular  decidua.  or  reflex  decidua:  the  remainder  is  the  uterine 
decidua,  or  decidua  parietalis. 

The  ovum  divides  and  redivides,  and  passes  down  the  oviduct 
toward  the  uterus.  By  the  time  the  ovum  reaches  this  organ  it  is 
5  mm.  in  diameter  and  the  mesoderm  has  appeared.  These  cells  form 
an  irregular  mass,  the  morula  (see  Fig.  226,  A).  The  outer  cells  of 
this  mass  arrange  themselves  beneath  the  zona  pellucida  as  the 
trophoderm,  or  outer  cell  mass,  while  the  remainder  constitute  the 
inner  cell  mass.  The  entire  structure  grows  rapidly,  and  the  inner  cell 
mass  becomes  differentiated  into  three  groups  of  cells,  the  ectodermal 
mass,  entodermal  mass  and  mesodermal  mass  (B,  Fig.  226).  Cavities 
appear  in  these  masses  through  the  vacuolization  and  disappearance 
of  some  of  the  cells.    That  within  the  ectodermal  mass  is  the  amniotic 

396, 


THE   PLACENTA   AND    UMBILICAL   CORD 


397 


A  B  C 

Fig.  226. 
A,  Morula — a,  Morular  cells;  b,  zona  pellucida.  B,  Later  stage — d,  Trophoderm; 
e,  ectodermal  mass;  f,  entodermal  mass;  g,  mesodermal  mass.  C — d,  Tro- 
phoderm; h,  amniotic  cavity;  i,  ectoderm;  c,  c'  indicate  respectively  the 
direction  of  the  cephalic  and  caudal  extremities  of  the  embryonic  area. 
The  trophoderm  is  shaded,  the  ectoderm  black,  the  entoderm  dotted  and 
the  mesoderm  lined. 


W-rgl 


Fig.  227. — n,  The  trophodermal  villi  penetrated  by  the  chorionic  mesoderm, 
representing  the  chorionic  villi;  o,  embryonic  shield;  p,  beginning  body- 
stalk. 


398 


PRACTICAL  HISTOLOGY 


cavity,  that  within  the  entoderm  the  enteric  and  that  within  the 
mesoderm  (extraembryonic)  the  celom  (C,  Fig.  226).  The  cavities  are 
rilled  with  liquid  and  the  entire  structure  is  called  the  triploblast 
or  blastodermic  vesicle.  During  these  internal  changes  the  tropho- 
derm  has  become  thickened  and  the  zona  pellucida,  having  per- 


Fig.   228. — n,  Chorionic  villi;  o,  embryonic  shield;  p,    body-stalk;   n,    amnion; 
s,  allantois;  t,  yolk-sac  with  vessels;  v,  blastopore.      Mesoderm  unmarked. 

formed   its   function,    has    disappeared.     The    ovum   has   become 
implanted  and  is  covered  by  the  decidua  capsularis. 

In  examining  C,  Fig.  226,  it  will  be  seen  that  at  first  the  ecto- 
dermal roof  of  the  amniotic  cavity  is  in  continuity  with  the  tropho- 
dermal  cells.  The  floor  of  the  amniotic  cavity  is  called  the  embry- 
onic shield,  ox  button  and  in  this  area  alone  the  embryo  is  developed. 


THE   PLACENTA   AND   UMBILICAL   CORD 


399 


Fig.  227  show  that  the  mesoderm  has  separated  the  ectoderm 
from  the  trophoderm  and  also  that  the  mesodermal  tissue  of  right 
wall  of  the  amniotic  cavity  has  been  increased.  This  is  of  sig- 
nificance. Fig.  228  shows  this  latter  tissue  greatly  increased  forming 
what  is  called  the  body  or  belly-stalk.  This  stalk  has  become  pro- 
nounced through  the  splitting  of  the  mesoderm  of  the  roof,  this 
cleft  extending  all  the  way  to  the  body-stalk  (Fig.  228).  This 
membrane  (ectoderm  and  mesoderm)  roofing  the  amniotic  cavity 
is  the  amnion,  the  formation  of  which  is  not  the  same  in  all  verte- 
brates. If  the  embryonic  shield  be  examined  it  will  be  found  to 
consist  of  ectoderm  and  entoderm  in  the  embryonic  area  proper,  the 
body  mesoderm  having  as  yet  not  been  developed. 


A  B 

Fig.  229. 
A — x,  Head-fold  of  the  amnion;  y,  tail-fold  of  the  amnion;  v,  notochordal  in- 
vagination (gastrulation)  of  ectoderm  beginning.  B — z,  Notochordal  canal. 
The  space  between  the  ectoderm  and  entoderm  is  exaggerated,  a",  Group 
of  ectodermal  cells,  around  the  blastopore,  that  gives  rise  to  the  body 
mesoderm. 

If  this  area  be  viewed  from  the  ectodermal  (dorsal)  side  a  linear 
groove  extending  over  the  greater  part  of  the  shield  will  be  noted. 
This  is  the  neural  groove.  This  groove  deepens,  its  dorsal  lips 
meet  and  fuse  and  thus  a  tube  of  ectoderm,  the  neural  tube,  is  buried 
beneath  the  ectoderm.  From  this  tube  the  entire  central  nerve 
system  is  developed. 


400 


PRACTICAL   HISTOLOGY 


At  the  cephalic  extremity  (left  in  Fig.  229,  A  and  B),  of  the  embry- 
onic area  a  slight  transverse  groove  (x)  appears  called  the  head 
fold  of  the  amnion.     This  marks  absolutely  the  head  limit  of  the 


4*   4r    4& 


^k^JLJk 


C  D 

Fig.  230. 

A — b',  Buccopharyngeal  membrane;  d',  neurenteric  canal;  z',  part  of  the  noto- 
chordal  canal,  shown  in  broken  line,  forming  posterior  wall  of  the  gut 
tract.  B,  Cross-section  of  A.  At  z,  the  notochordal  canal  is  shown  by  a 
broken  line.  C — b,  Buccopharyngeal  membrane;  d',  neurenteric  canal; 
z',  completed  notochord.  D,  Cross-section  of  C  showing  the  notochord 
completed.      The  white  or  lined  spaces  indicate  mesoderm. 

embryo.  At  the  caudal  extremity  (right  in  Fig.  229,  A  and  B),  a 
like  groove  (y)  appears,  the  tail  fold  of  the  amnion.  Two  lateral 
linear  grooves  appear  called  the  lateral  folds,  limiting  the  body 
laterally  (Fig.  230,  B  and  D).     As  those  folds  deepen  and  approach  one 


THE    PLACENTA   AND   UMBILICAL   CORD 


401 


another  ventrally  the  body  is  completely  outlined.  The  ectoderm 
and  mesoderm  form  a  layer  called  the  somatopleure  (Fig.  231), 
that  gives  rise  to  the  amnion  and  body  wall.  The  entoderm  and 
mesoderm  constitute  a  layer,  the  splanchnopleure,  which  gives  rise 
to  the  gut-tract,  yolk-sac,  vitelline  duct  and  allantois. 

As  seen  in  the  foregoing  the  ectoderm,  entoderm  and  extraembry- 
onic mesoderm  have  been  formed  from  solid  masses  by  the  disap- 
pearance of  certain  of  their  cells,  or  delamination  as  it  is  called.  The 
body  or  intraembryonic  mesoderm  is  formed  in  another  manner. 
At  the  caudal  end  of  the  neural  groove  a  small  depression  appears 


n  m  I  k        i  h  g 

Fig.  231. — Section  of  a  Chick  Embryo  with  Eight  Segments. 

(Balfour.) 

a,  lateral  fold  of  the  amnion;  b,  somatopleuric  mesoderm;  c,  muscle  plate;  d, 
mesoderm  of  somite;  e,  intraembryonic  celom;  /,  extraembryonic  celom; 
g,  splanchnopleuric  mesoderm;  h,  primitive  kidney  anlage;  i,  aorta;  k, 
notochord;  I,  entoderm  of  gut-tract;  m,  vessel;  n,  entoderm  of  yolk-sack. 

due  to  the  cord-like  invagination  of  ectoderm  between  ectoderm 
and  entoderm.  This  is  the  notochordal  invagination  and  this  con- 
stitutes a  modified  gaslrulation  (Figs.  228  and  229).  The  mass  of 
ectoderm  continues  to  grow  cephalad  to  within  a  short  distance  of 
the  head  end  of  the  neural  tube,  to  which  it  lies  ventral.  This  cord 
becomes  a  tube  by  the  disappearance  of  its  central  cells  and  then 
its  ventral  wall  and  the  entoderm  (against  which  it  lies)  both  dis- 
appear, thereby  (Fig.  230,  A  and  B,  Z')  making  the  notochordal 
ectoderm  the  dorsal  boundary  of  the  enteric  cavity,  and  leading 
former  observers  to  believe  that  the  notochord  arose  from  the  en- 

26 


402  PRACTICAL  HISTOLOGY 

toderm.  Soon  the  notochordal  ectoderm  folds  off  from  the  entoderm 
forming  a  solid  cord  (Fig.  230,  C  and  D,  Z")  the  notochord  proper. 
When  the  notochordal  cavity  became  continuous  with  the  enteric 
cavity  this  later  cavity  communicated  with  the  amniotic  cavity 
through  notochordal  depression;  this  short  canal  is  called  the  neur en- 
teric canal,  because  the  neural  tube  ultimately  closes  off  the  amniotic 
connection  and  then  the  canal  leads  from  the  neural  canal  into  the 
enteric  canal. 

As  the  notochordal  invagination  is  formed  other  ectodermal 
cells  are  set  aside  here  between  ectoderm  and  entoderm.  These 
begin  to  multiply  rapidly  forming  an  entirely  different  group  of  cells 
that  spread  in  all  directions  between  ectoderm  and  entoderm, 
constituting  the  body  mesoderm  that  soon  connects  with  the  extra- 
embryonic mesoderm. 

By  this  time,  the  ovum  has  become  lodged  in  the  uterine  mucosa. 
This  process  is  accomplished  by  the  aid  of  the  trophodermal  cells, 
that  have  the  power  of  phagocytosis  (destruction  of  tissue)  and  erode 
the  superficial  tissues  of  the  mucosa,  forming  a  cavity  into  which 
the  ovum  sinks.  The  trophodermal  layer  has  become  increased  in 
thickness.  The  epithelium  of  the  uterus  is  lost  in  this  region  and  also 
in  the  glands  and  the  superficial  vessels  are  exposed.  The  tropho- 
derm,  or  placentoblast  becomes  altered  as  follows:  Cells  vacuo- 
late and  disappear  at  irregular  intervals  leaving  a  fringe  of  epithe- 
lial villi,  the  trophodermal  villi.  As  a  result,  there  are  formed  a 
series  of  intercommunicating  spaces,  the  trophodermal  lacuna.  Ac- 
cording to  some  the  trophoderm  first  consists  of  two  layers  of  cells. 
These  increase  in  an  irregular  manner  forming  little  finger-like 
projections,  the  trophodermal  villi.  When  these  become  invaded 
by  the  mesoderm  they  constitute  chorionic  villi.  The  villi  are  com- 
posed of  trophoderm  and  mesoderm.  When  the  vessels  of  the 
mucosa  are  exposed,  they  rupture  into  the  glandular  spaces,  and 
from  these,  the  maternal  blood  gains  access  to  the  trophodermal 
lacuna,  or  spaces.  Thus  does  the  embryo  receive  nourishment  from 
the  mother,  before  the  umbilical  vessels  are  present.  The  area  of 
the  ovum  left  uncovered  when  the  ovum  becomes  lodged,  is  covered 
by  mucosa  that  is  reflected  from  the  lining  at  the  sides  of  the  ovum. 
This  is,  therefore,  called  decidua  capsulaiis  or  ovular  decidua.     The 


THE   PLACENTA   AND   UMBILICAL   CORD 


403 


trophodermal  villi  soon  receive  a  core  of  mesoderm  and  are  then  called 
chorionic  villi,  the  whole  membrane  being  termed  the  Chorion. 

We  must  remember  that  the  belly-stalk  connects  the  embryo 
with  the  chorion.  This  belly-stalk  is  of  importance,  because  it 
presents  that  part  of  the  embryonic  disc  that  does  not  lose  connection 


Fig.  232. — Semi-diagrammatic  Outline  of  a  Dorso-ventral  Section  of  a 
Human  Uterus  Containing  an  Embryo  of  about  Five  "Weeks. 

a,  Ventral;  p,  dorsal  surface;  g,  outer  limit  of  decidua;  s,  s,  limits  of  the  placental 
decidua;  ch,  chorion,  within  which  is  the  embryo  enclosed  by  the  amnion, 
and  attached  to  the  chorion  by  the  umbilical  cord;  from  the  cord  hangs  the 
pedunculated  yolk-sac;  r,  r,  ovular  decidua.     (Minot.) 


with  the  prochorion  during  the  formation  of  the  body-wall  and  gut- 
tract.  Into  the  belly-stalk  the  allantoic  evagination  of  the  gut-tract 
extends  for  a  short  distance,  while  the  allantoic  vessels  pass  along 
the  entire  extent  of  the  stalk  to  the  forming  chorion.  With  the 
passage  of  the  allantoic  vessels  to  vascularize  the  chorion,  the  belly- 


404  PRACTICAL   HISTOLOGY 

stalk  becomes  the  so-called  extraembryonic  portion  of  the  allantois.  In 
some  animals,  the  oviparous,  the  allantois  develops  as  an  independ- 
ent sac  there  being  no  belly-stalk  in  those  forms.  It  remains  as  a 
dilated  sac,  and  serves  as  a  receptacle  for  urine.  In  the  viviparous 
animals,  it  remains  connected  with  the  belly-stalk,  and  is  said  to  con- 
nect the  embryo  with  the  uterus,  becoming  the  organ  of  nutrition  and 
respiration.  As  a  matter  of  fact,  it  is  the  belly-stalk  that  forms  the 
link  between  fetus  and  chorion;  the  chorion  becomes  the  fetal  portion 
of  the  placenta,  while  the  belly-stalk  becomes  the  umbilical  cord  by 
the  addition  of  the  vessels.  It  would  seem  that  the  allantois  proper 
has  nothing  to  do  with  the  formation  of  the  placenta  and  cord  in  the 
higher  types.  In  this  mesoderm,  four  main  vessels  develop,  two 
arteries  and  two  veins.  Later  but  one  vein  is  found,  due  either  to  a 
fusion  of  the  two  veins,  or  probably  to  the  atrophy  of  the  right  vein. 
The  two  veins  enter  the  body  and  proceed  toward  the  heart,  while 
the  other  two  vessels  pass  into  the  body,  and  connect  with  the  aorta. 
The  distal  ends  of  all  the  vessels  pass  into  the  chorion,  and  divide  to 
ramify  all  the  villi.  These  villi  are  still  covered  by  the  trophoderm, 
consisting  usually  of  two  layers.  Of  these,  the  outer  becomes  con- 
verted into  a  thin  layer  of  protoplasm,  in  which  the  original  nuclei 
remain  and  the  cell-boundaries  are  lost.  This  protoplasm  con- 
stitutes the  syncytium. 

The  villi  do  not  remain  simple,  but  branch  and  rebranch;  the 
vessels  follow  these  branches,  and  penetrate  to  the  very  ends. 
Some  of  the  villi  enter  the  uterine  glands,  in  which  the  epithelium 
becomes  denuded  by  about  the  sixth  week,  and  the  surface  cells  by 
the  fourth  week,  and  are  the  floating  villi;  others  become  attached, 
and  form  the  fixed  villi.  When  the  epithelium  of  the  uterus  is  lost, 
the  engorged  superficial  capillaries  of  the  placental  decidua  become 
connected  with  the  glands,  and  the  blood  enters  these,  and  then 
the  trophodermal  spaces.  These  channels  are  the  later  intervillous 
spaces.  From  these  cavities,  the  blood  is  returned  to  the  venous 
channels  of  the  mucosa,  but  no  direct  connection  is  established  between 
the  fetus  and  the  mother. 

These  villi  are  very  abundant,  and  may  be  scattered  all  over  the 
ovum  or  be  limited  to  the  equator  of  the  mass.  Up  to  this  time, 
all  are  equal  in  size.     Soon  a  difference  is  noted  in  size,  those  at  the 


THE   PLACENTA   AND   UMBILICAL   CORD 


405 


place  of  attachment  of  the  ovum  increase  in  number  and  size, 
forming  the  chorion  f rondo  sum  (the  later  placenta),  while  the  remain- 
der disappear  and  constitute  the  chorion  lave.  The  latter  do  not 
become  vascularized. 


Fig.  233. — Human  Placenta  at  Term. 

A,  Vertical  section  at  margin;  D,  decidua;  Cho,  chorion;  Fib,  fibrin;  Vi,  placental 

villi;  Si,  marginal  sinus;  vi,  aborted  extra-placental  villi;  b,  decidual  tissue. 

B,   Portion  of  decidual  tissue  at  b  highly  magnified;  v,   blood-vessels;  d, 

decidual  cells  with  one  nucleus;  d' ',  multinucleated  decidual  cells.     (Minot.) 


At  about  the  fifth  month,  a  villus  has  the  following  appearance. 
Of  the  trophodermal  cells,  the  outer  do  not  remain  large,  distinct 
elements,  but  become  flattened,  and  represent  a  mere  layer  of 
nucleated  protoplasm  that  covers  the  villi;  this  is  the  syncytium, 
and  it  is  the  covering  of  the  embryonic  connective  tissue  that  con- 


406 


PRACTICAL   HISTOLOGY 


stitutes  the  core  of  the  villi  and  supports  the  vessels.  In  the  inner 
layer,  the  cells  remain  distinctly  outlined,  and  persist  for  a  short 
time  as  the  cell-layer  of  Langhans.  From  the  fifth  month  on,  this 
layer  disappears  so  that  ultimately  only  the  syncytium  remains. 
Here  and  there  on  the  villi  are  seen  groups  of  cells  that  represent 
collections  of  syncytial  cells,  the  cell  knots.  These,  like  the  other 
syncytium,  contain  nuclei  that  are  small,  but  stain  deeply.     The 


Fig.  234. — Cross-section  of  some  Villi  of  the  Placenta  at  the  Fifth 

Month. 

a,   Syncytium;     b,   cell    layer    of    Langhans;     d,  mesenchymal    core    of    villus. 

(Photograph.     Obj.  4,  mm.,  oc.     5  X.) 

cytoplasm  responds  well  to  the  acid  stains.  The  Langhans  cells, 
however,  contain  large  nuclei,  but  neither  these  nor  the  cytoplasm 
respond  well  to  stains. 

After  the  third  month,  the  number  of  villi  that  becomes  attached 
to  the  mucosa  rapidly  increases,  so  that  after  that  time  the 
fetal  and  maternal  portion  become  more  and  more  fixed  to  each 
other. 

This  is  the  beginning  of  the  formation  of  the  placenta  as  it  is 
seen  at  birth.  The  villi  branch  repeatedly,  and  the  whole  structure 
grows  rapidly,  causing  the  child  to  do  the  same.     Any  disturbance 


THE   PLACENTA   AND   UMBILICAL   CORD  407 

that  will  retard  the  growth  of  the  placenta  will  also  retard  the 
growth  of  the  fetus  in  greater  proportion.  The  difference  between 
the  placenta  at  the  fourth  or  fifth  month  and  at  birth  is  merely  in 
size.  This  is  due  to  the  increase  in  number  and  branches  of  the  villi. 
The  villi  are  separated  into  groups  by  connective  tissue  septa  that 
are  derived  from  the  uterine  tunica  propria.  These  are  the  placental 
septa  and  they  contain  the  decidual  cells. 

At  birth  the  placenta  is  a  flesh-like,  saucer-shaped  mass,  the 
attached  surface  of  which  is  divided  into  lobes,  or  cotyledons.  The 
fetal  surface  is  covered  by  the  amnion,  a  continuation  of  the  sac  in 
which  the  fetus  lies,  and  shows  the  vessels  as  they  enter  and  leave 
the  organ;  the  opposite  surface  is  divided  into  lobes,  or  cotyledons, 
covered  by  the  decidua  basilaris.  The  weight  of  the  placenta  is 
from  500  to  1200  grams,  averaging  about  one-sixth  that  of  the 
child.     It  consists  of  two  portions,  the  fetal  and  maternal. 

This  organ  consists  of  a  fleshy  mass  lying  between  two  membranes. 
Upon  the  fetal  surface,  we  find  the  amnion  and  chorionic  mesoderm. 
The  amnion  consists  of  a  single  layer  of  cuboidal  epithelial  cells 
that  rest  upon  the  mesodermal  tissue.  These  epithelial  cells 
possess  prominent,  deeply-staining  nuclei,  but  the  cytoplasm  does 
not  react  well  to  the  stain.  The  mesodermal  tissue  is  somewhat 
fibrillar,  and  few  cells  are  present.     It  is  avascular. 

The  chorionic  mesoderm  is  composed  of  mesodermal  tissue  in 
which  the  fibrils  are  more  or  less  distinct.  This  mesoderm  is  covered 
by  trophodermal  (ectodermal)  cells  that  later  become  the  syncytium. 
From  the  side  opposite  to  the  amnion  are  seen  projections.  These 
may  vary  from  small  simple  villi  to  those  resembling  a  tree  possessing 
an  enormous  number  of  twigs.  Along  this  surface  of  the  chorion, 
may  be  seen  masses  of  a  fibrillar  substance  that  are  called  canalized 
fibrin.  The  bulk  of  the  placenta  consists  of  villi.  These  form  a 
reddish  spongy  mass,  divided  into  masses  called  cotyledons.  The 
main  stems  contain  two  or  more  vessels  surrounded  by  mesodermal 
tissue.  Peripherally,  each  villus  is  covered  by  a  thin  layer  of 
nucleated  protoplasm,  the  syncytium.  The  small  twigs  consist  of  a 
core  of  mucous  connective  tissue  supporting  several  small  capillaries. 
The  syncytium  surrounds  each  twig.  In  places  are  seen  collections 
of  nuclei  representing  the  cell-knots.     The  cavities  between  the  villi 


408  PRACTICAL  HISTOLOGY 

are  the  intervillous  spaces  containing  the  maternal  blood  and,  at 
times,  canalized  fibrin. 

From  this,  it  is  readily  seen  that  the  fetal  and  maternal  blood 
currents  do  not  intermingle.  They  are  separated  from  each  other, 
the  endothelium  of  the  fetal  capillaries  on  the  one  hand,  and  the 
syncytium  of  the  villi  on  the  other. 

The  maternal  side  of  the  placenta  is  covered  by  the  decidua 
basalis,  or  the  stratum  compactum  of  the  mucosa.  It  is  less  than 
a  millimeter  thick,  and  possesses  a  number  of  short  oblique  channels. 
These  are  the  remains  of  the  uterine  glands;  they  now  represent 
blood  sinuses,  which  contain  maternal  blood. 

The  basalis  extends  into  the  fetal  portion  as  the  placental  septa,  . 
and  divides  it  into  the  cotyledons.  At  the  edge  of  the  placenta,  it 
becomes  attached  to  the  chorion,  and  continues  as  the  decidua 
parietalis.  At  this  junction  there  is  a  considerable  space  that 
extends  all  around  the  edge  of  the  placenta.  This  is  the  marginal 
sinus,  and  is  prominent  because  few  or  no  villi  have  developed  here. 

The  membranes  consist  of  the  amnion  and  the  uterine  lining,  or 
the  stratum  compactum.  The  latter  is  thin,  and  contains  neither 
glands  nor  epithelium.  When  the  fetus  increases  in  size  and  causes 
a  dilatation  of  the  uterus,  the  amniotic  sac  is  forced  against  the 
uterine  lining,  and  causes  an  atrophy  of  the  glands  and  cells  of  the 
stratum  compactum.  As  a  result,  a  mere  fibrinous  membrane,  that 
has  a  loose  connection  with  the  amnion,  is  produced,  due  entirely 
to  pressure. 

Fossati,  by  means  of  the  Golgi  method,  found  a  peculiar  network 
of  fibers  surrounding  the  blood-vessels  of  the  placenta  and  umbilical 
cord;  this  network  also  seemed  to  come  into  relation  with  the 
epithelium.     He  considered  this  network  nerve  tissue. 

There  are  four  varieties  of  placentae:  (i)  Villous,  in  which  the 
villi  simply  fit  into  the  uterine  glands,  as  in  the  pig  and  armadillo. 

(2)  Cotyledonary,  in  which  the  placenta  consist  of  many  scattered 
button-  or  ring-like  masses,  as  in  the  cow,  horse,  camel  and  sheep. 

(3)  Zonary,  in  which  the  placenta  is  a  band-like  mass  surrounding 
the  uterine  tube  transversely,  as  in  the  cat  and  dog.  (4)  Discoidal, 
in  which  the  placenta  is  a  discoidal  mass,  as  in  man  and  rodents. 

The  umbilical  cord  is  the  connecting  link  between  the  fetus  and 


THE   PLACENTA   AND    UMBILICAL   CORD  409 

the  placenta,  and  represents  the  early  belly-stalk.  It  is  peculiarly 
twisted  and  may  even  be  knotted.  It  is  surrounded  by  one  or  more 
layers  of  cuboidal  epithelial  cells,  continuous  on  the  one  hand  with 
epithelium  of  the  amnion,  and  on  the  other  with  the  ectodermal  cells  of 
the  body,  supported  by  a  little  subepithelial  fibrous  tissue.  Within 
this  covering  is  the  peculiar  tissue  called  Wharton's  jelly.  This  is 
embryonic  connective  tissue  in  which  the  cells  are  chiefly  spindle- 
shaped;  some  round  and  stellate  cells,  however,  are  seen.  The 
intercellular  substance  is  semi-solid,  and  takes  a  peculiar  homo- 
geneous stain.  During  the  early  months  of  pregnancy,  the,  inter- 
cellular substance  contains  a  great  deal  of  water,  and  the  cellular 
elements  are  few.  At  the  end  of  pregnancy  the  intercellular  sub- 
stance is  somewhat  fibrillar,  though  the  semi-solid  portion  pre- 
dominates. At  this  time  the  cells  are  mostly  of  the  stellate  type, 
but  not  numerous.  At  the  body  end,  occasionally,  traces  of  allantoic 
cavity  and  yolk  sac  are  found. 


Fig.  235. — Cross-section  of  Human  Umbilical  Cord.     (Minol.) 
t       A,  A',  Umbilical  arteries;  V,  umbilical  vein;  Y,  remains  of  allantois. 

The  vessels  contained  are  the  single  umbilical  vein  and  two 
umbilical  arteries.  These  are  all  thick-walled  and  well-developed, 
and  the  muscle  fibers  run  both  circularly  and  longitudinally.  The 
wall  of  the  arteries  is  thicker  than  that  of  the  vein.  The  insertion  of 
the  cord  into  the  placenta  is  usually  eccentric,  and  at  this  point  the 
vessels  branch  rapidly  and  spread  out  in  all  directions. 

The  circulation  of  the  placenta  is  a  closed  one.  The  blood  is 
carried  from  the  iliac  arteries  to  the  umbilicus  through  the  hypogastric 
arteries,  which  continue  in  the  cord  as  the  umbilical  arteries.     These 


4IO  PRACTICAL   HISTOLOGY 

branch  to  follow  the  villi  and  ultimately  terminate  in  tufts  of  capil- 
laries in  the  terminal  villous  twigs.  The  blood  at  this  point  receives 
the  oxygen  and  nutritive  matter  from  the  maternal  blood  that 
circulates  in  the  intervillous  spaces  in  which  the  villi  lie.  There 
is  no  direct  communication  between  the  fetal  and  maternal  blood,  for 
they  are  separated  from  each  other  by  the  endothelium  of  the  capil- 
laries and  the  syncytium  covering  the  villi.  As  the  oxygen  and 
nutritious  substances  pass  into  the  fetal  blood,  the  effete  matter  and 
gases  pass  out  into  the  maternal  blood.  The  principle  is  the  same 
as  in  the  lung,  where  the  blood  is  oxygenated.  Red  cells  never  pass 
from  one  system  to  another,  but  leukocytes  that  have  the  power  of 
ameboid  motion  may.  The  blood  is  collected  by  the  radicals  of  the 
umbilical  vein  and  carried  into  the  body  to  the  under  surface  of  the 
liver,  where  a  portion  enters  the  portal  vein  through  the  continuation 
of  the  umbilical  vein,  is  distributed  to  the  liver  and  collected  by  the 
hepatic  veins  and  emptied  into  the  postcava;  the  remainder  is 
carried  to  the  postcava  (inferior  vena  cava)  by  the  ductus  venosus. 
The  blood  passes  to  the  right  atrium,  then  through  the  foramen 
ovale  to  the  left  atrium,  from  which  it  passes,  through  the  atrio- 
ventricular orifice,  into  the  left  ventricle.  The  blood  then  passes 
into  the  aorta  chiefly  to  the  upper  extremities  and  head,  is  collected 
by  the  radicals  of  the  precava  (superior  vena  cava),  and  emptied 
into  the  right  atrium.  From  this  chamber  it  passes  through  the 
atrio-ventricular  orifice  into  the  right  ventricle,  from  which  it 
passes  into  the  pulmonary  artery  toward  the  lungs.  As  these  organs 
do  not  functionate  at  this  time,  most  of  the  blood  is  sent  to  the  aorta 
through  the  di  ctns  arteriosus.  The  blood  then  passes  toward  the 
lower  extremities,  and,  as  it  reaches  the  internal  iliac  arteries,  most 
of  it  is  sent  to  the  placenta  through  the  arterial  trunks,  which  inside 
of  the  body  are  called  the  hypogastric  arteries,  and  in  the  cord  the 
umbilical  arteries. 


CHAPTER  XVI 
THE  SKIN  AND  ITS  APPENDAGES 

The  skin  covers  the  external  surface  of  the  body  and  is  its  most 
extensive  organ.  It  varies  in  thickness  in  the  different  parts;  upon 
the  medial  surfaces  of  the  extremities  it  is  thinnest  and  gradually 
increases  in  thickness  over  the  thorax,  abdomen,  lateral  surfaces 
of  the  extremities,  back,  buttock,  palm  and  sole. 

It  consists  of  two  portions,  the  epidermis,  or  cuticle,  and  the  cutis 
vera,  or  corium.  The  epithelial  portion  is  the  protective  part  while 
the  connective  tissue  derma  is  the  vascular  portion  and  also  contains 
the  accessory  structures.  The  skin  besides  being  protective  is  also 
very  sensitive;  in  the  derma  are  the  tactile  organs  and  various  other 
sensor  nerve  organs  for  the  perception  of  general  sensations,  pain 
and  temperature  changes.  It  is  also  an  important  excretory  organ 
and  maintains,  or  regulates  body  temperature.  It  has  a  number 
of  different  appendages.  The  hairs  serve  as  a  protection  and  are 
not  evenly  distributed,  as  will  be  seen  later.  The  sebaceous  glands 
secrete  an  oil  that  serves  to  keep  the  skin  pliable  and  tends  to  keep 
the  hairs  soft  and  flexible.  The  sweat  glands  have  a  double  function; 
they  are  excretory  glands  and  are  assistants  to  the  kidneys.  The 
perspiration  also  serves  to  regulate  the  body  temperature.  The 
nails  are  protective.  These  appendages  lie  wholly  or  nearly  so, 
except  the  shafts  of  the  hairs,  within  the  vascular  derma. 

In  general  pigment  is  lacking  in  the  skin  of  the  Caucasian  except 
around  the  nipples  and  genitalia  and  in  those  individuals  who  live 
in  the  tropical  and  subtropical  regions.  Pigment  is  deposited  in 
those  individuals  as  a  protection  against  the  actinic  rays  of  the  sun. 
The  general  pinkish  color  is  due  to  the  vascularity  of  the  derma  and 
the  thicker  the  epidermis  the  lighter  the  color.  The  skin  is  con- 
tinuous with  the  mucous  membranes  of  the  body  at  the  various 

411 


412 


PRACTICAL   HISTOLOGY 


orifices  of  the  various  tracts,  as  the  oral  and  nasal  apertures  and  the 
anal  and  urinogenital  orifices.  At  these  mucocutaneous  junctions  the 
skin  is  more  delicate  and  more  vascular  and  the  transition  from  skin 
to  mucous  membrane  is  sharp  and  distinct. 


Fig.  236. — Skin  of  the  Palm  of  a  Child  at  Birth  Showing  Stratified 
Squamous  Epithelium.  (Radasch,  Reference  Handbook  of  the  Medical 
Sciences.) 

The  epidermis  is  the  epithelial  portion  of  which  the  appendages 
are  modifications.  It  varies  in  thickness  from  0.03  mm.  to  over 
1  mm.  in  different  parts  of  the  body.  This  is  in  direct  proportion 
to  the  amount  of  mechanical  disturbance  to  which  the  part  is  sub- 
jected.    It  consists  of  stratified  squamous  cells,   which,   over  the 


THE    SKIN   AND   ITS    APPENDAGES 


413 


general  body  surface,  are  divisible  into  two  layers,  stratum  Malpighii 
and  stratum  corneum. 

The  stratum  Malpighii,  or  rete  mucosum,  is  composed  of  a  number 
of  layers  of  cells.  The  basal  part  consists  of  columnar  elements, 
and  is  called  the  genetic  layer.  The  cells  stain  deeply,  and  under 
certain  conditions  show  pigment  granules.  The  layer  is  uneven  in 
its  course,  as  it  conforms  to  the  waves  of  the  corium.  The  upper 
cells  of  the  stratum  Malpighii  are  large  polyhedral  elements  that 
do  not  touch  one  another,  but  are  separated  by  intercellular  spaces. 
These  spaces  form  an  extensive  area  for  the  diffusion  of  lymph  and 
are  bridged  by  delicate  cytoplasmic  processes  that  extend  from  one 


Fig.  237. — Stratified  Squamous  Cells  Showing  Prickle  Cells. 
(Radasch,  Reference  Handbook  of  the  Medical  Sciences.) 


cell  to  another.  This  is  sometimes  called  the  stratum  spinosum. 
These  are  prickle  cells  that  are  also  seen  in  other  stratified  layers. 
As  the  upper  part  of  this  stratum  is  approached,  the  cells  become 
flattened  and  have  an  even  course.  Very  often  the  uppermost 
layers  of  cells  contain  granules  constituting  the  stratum  granulosum 
to  be  described  later. 

The  stratum  corneum  ordinarily  forms  a  thin  layer.  Its  cells 
are  very  thin  and  scale-like  and  usually  possess  no  nuclei.  They  are 
derived  from  the  cells  beneath,  but  differ  from  them  in  consisting 
of  keratin,  or  pareleidin,  that  gives  them  their  hard  and  horny 
characteristic.  This  substance  is  shiny  and  highly  refractile,  and 
does  not  respond  readily  to  ordinary  stains.     These  cells  are  con- 


414  PRACTICAL  HISTOLOGY 

stantly  cast  off,  and  the  cells  below  increase  to  replace  them.  The 
cells  of  the  lower  layers  acquire  a  distinct  exoplasmic  zone,  the 
prickles  become  shorter  and  thicker  and  the  nucleus  shrunken  and 
dried. 

Over  the  general  cutaneous  surface  the  cells  of  the  stratum  corneum 
are  scale-like  and  no  longer  resemble  cells.  When  treated  with  a 
solution  of  potassium  hydroxid  they  swell  and  appear  vesicular. 
Upon  the  sole  and  palm  the  cells  of  the  stratum  corneum  are  larger 
and  appear  swollen.  They  represent  the  epitricheal  cells  of  the 
fetus  which  seem  to  persist  in  those  parts  devoid  of  hairs. 

In  certain  parts  of  the  body,  sole  and  palm,  the  stratum  granu- 
losum  and  another,  the  stratum  lucidum,  are  well  developed. 

The  stratum  granulosum  lies  exernal  to  the  stratum  Malpighii, 
and  is  composed  of  two  or  three  layers  of  flattened,  spindle-shaped 
cells  that  contain  a  deeply  staining  nucleus  and  coarsely  granular 
cytoplasm.  The  granules  are  keratohyalin  that  later  form  the  horny 
matter  of  the  stratum  corneum.  This  substance  is  peculiar  to 
mammals.  These  granules  are  quite  large  and  prominent,  and  re- 
spond well  to  hematoxylin  as  it  is  strongly  basophilic.  They  seem  to 
be  modified  cytoplasm,  but  some  hold  that  they  represent  products 
of  the  nucleus  but  not  chromatin. 

The  stratum  lucidum  lies  external  to  the  stratum  granulosum,  and 
separates  this  from  the  stratum  corneum.  It  forms  a  narrow, 
glistening  band  of  cells,  two  or  three  layers  broad,  in  which  the 
keratohyalin  granules  have  fused  to  form  a  homogeneous  substance, 
called  eleidin.  In  the  stratum  corneum  these  granules  become 
pareleidin;  this  will  blacken  slowly  in  osmic  acid  due  to  the  oil  from 
the  glands,  not  fat  in  the  cells.  This  substance  reacts  well  to 
eosin.  The  nuclei  are  not  prominent  nor  are  the  cell-bodies  dis- 
tinct.    This  layer  is  absent  where  the  skin  is  thin. 

As  the  cells  of  the  stratum  corneum  are  constantly  desquamating 
they  must  be  replaced.  This  is  brought  about  by  active  karyo- 
kinesis  of  the  cells  of  the  stratum  Malpighii. 

In  injuries  to  the  skin  where  the  epidermis  is  lost  the  stratum 
Malpighii  at  the  margins  of  the  area  gradually  extend  onto  the 
injured  area  and  from  this  extension  the  special  layers  are  later 
derived.     When  the  denuded  area  is  great  skin-grafting  is  employed. 


1111     SKIN    AND   ITS   APPENDAGES 


415 


In  this  each  minute  graft  represents  a  little  island  from  which  the 
stratum  Malpighii  spreads  in  all  directions  and  the  denuded  area 
ultimately  becomes  entirely  covered  if  the  work  is  successful. 

The  derma,  true  skin,  or  cutis  vera,  is  composed  of  connective 
tissue  arranged  in  two  or  more  less  distinctly  separated  layers. 


■-~v 


.- 


'&>.■  '■'.■  •.'.'■;'  *.';'»'; 


VrF 


■mm* 

£<<£    '  /■■/ 

Fig.  238. — Cross-section  of  Skin  of  Sole  of  Foot. 
a,  Stratum  corneum;  b,  stratum  lucidum;  c,  stratum  granulosum;  d,  stratum 
Malpighii;  e,  derma;  /,  panniculus  adiposus;  g,  duct  of  sweat  gland;  h, 
prickle  cells;  i,  genetic  layer;  k,  cross-section  of  a  smooth  muscle  fiber; 
/,  duct  of  sweat  gland;  m,  Pacinian  body;  n,  secretory  portion  of  sweat 
gland;  o.  muscle  of  tubule;  p,  blood-vessel;  q,  adipose  tissue. 

These  are  the  stratum  papillare,  or  outer,  and  the  stratum  recticulare, 

or  inner. 

The  stratum  papillare  consists  of  delicate  bundles  of  small  white 
fibrils  forming  a  close  network  with  elastic  fibers. 

The  upper  portion  of  this  stratum  is  thrown  into  small  waves 


41 6  PRACTICAL  HISTOLOGY 

called  the  papilla;,  to  which  the  stratum  Malpighii  conforms.  Over 
the  general  skin  surface,  these  papillae  do  not  extend  through  the 
stratum  Malpighii,  but  in  the  palmar  and  plantar  regions  they  are 
visible  externally,  and  assist  in  forming  the  peculiar  markings  seen 
in  these  areas.  These  papillae  are  important,  as  they  contain  either 
capillary  plexuses  or  special  sensor  nerve  organs.  These  are  the 
vascular  and  tactile  papillce,  respectively.  The  lower  portion  of  the 
papillare  consists  of  a  looser  network,  in  which  the  vessels  form 
plexuses  parallel  with  the  surface.  It  gradually  passes  into  the 
stratum  reticulare.  These  papillae  are  tallest  and  most  numer- 
ous in  the  palmar  and  plantar  regions,  poorly  developed  in  the 
skin  of  the  face  and  here  tend  to  disappear  in  old  age.  In  the 
palmar  and  plantar  regions  there  are  usually  two  papillae  under 
each   ridge. 

The  stratum  reticulare  is  not  distinctly  separable  from  the  pre- 
ceding. It  is  composed  of  larger  bundles  of  coarser  fibrils  of  white 
fibrous  tissue,  and  contains  some  yellow  elastic  tissue,  as  will  be  seen 
below.  Here  are  found  the  larger  blood-vessels  and  the  appendages 
and  special  sensor  nerve  beginnings.  In  the  corium  of  the  scrotum, 
penis  and  nipple,  smooth  muscle  fibers  are  found.  When  these 
bundles  contract,  "  goose-flesh"  is  produced.  In  the  skin  of  the 
face  and  over  joints  elastic  tissue  is  most  abundant.  It  decreases 
everywhere  with  old  age. 

The  elastica  is  often  separated  into  layers,  of  which  there  are  four, 
the  subepithelial,  papillary,  reticular  and  subcutaneous  elastic  layers. 
In  the  scrotum  they  form  a  membranous  layer. 

The  derma  varies  in  thickness  from  0.5  mm.  to  5  or  6  mm.;  the 
latter  measurement  represents  that  of  the  derma  of  the  back  and 
shoulders.  Here  this  layer  is  quite  dense  and  many  of  the  bundles 
of  white  fibrous  tissue  pass  vertically  through  it  to  the  panniculus 
adiposus. 

Beneath  the  stratum  reticulare  is  the  subcutaneous  tissue,  or  pan- 
niculus adiposus.  This  varies  in  thickness  and  density  in  the  various 
parts  of  the  body  and  the  amount  of  fat  is  also  variable.  It  connects 
the  skin  to  the  deep  or  muscle  fascia  and  its  mobility  varies.  It  con- 
sists of  bundles  and  septa  of  coarse  white  fibrous  tissue  forming 
meshes  that  contain  the  adipose  tissue.     The  latter  is  usually  in  the 


THE    SKIN   AND   ITS    APPENDAGES  417 

form  of  lobules  of  different  sizes.  In  some  regions  of  the  body  the 
bundles  course  nearly  parallel  to  the  skin  and  here  the  meshes  are 
larger  and  the  skin  is  more  mobile.  Where  the  bundles  are  more 
vertical  the  skin  is  more  firmly  held.  In  addition  to  the  cutaneous 
nerves  and  vessels  this  layer  contains  the  roots  of  the  larger  hair 
follicles,  and  the  larger  sebaceous  and  sweat  glands.  Haggquist  has 
described  a  thick  bundle  of  smooth  muscle  tissue  at  the  boundary 
zone  between  the  stratum  reticulare  and  subcutaneous  tissue  in 
those  regions  called  cold  spots  and  not  elsewhere.  By  the  reflex 
contraction  of  this  muscle  the  adjacent  blood-vessels  are  constricted 
when  the  skin  here  is  subjected  to  a  cold  object. 

Very  little  elastic  tissue  is  present  in  this  layer  and  granules  have  been 
found  in  the  corium.  In  the  white  races,  this  pigmentation  is  limited 
to  the  nipple  and  genital  region.  In  the  colored  races  the  amount 
of  pigmentation  gives  the  varying  degrees  of  depth  of  color.  In  the 
lighter  individuals  the  pigment  {melanin)  is  limited  to  the  lower 
layers  of  the  stratum  Malpighii  but  as  the  color  deepens  not  only  is 
there  more  pigment  but  more  layers,  higher  up,  are  involved  and  the 
connective  tissue  cells  of  the  derma  will  contain  increasing  amounts 
of  pigment. 

In  the  colored  races  the  pigmentation  of  the  skin  is  not  manifested 
for  several  days  after  birth,  although  the  pigment  is  present  for 
several  wreeks  before  birth.  Whether  the  pigment  is  due  to  the 
vital  activity  of  the  cells,  or  whether  it  is  brought  here  and  deposited, 
is  not  definitely  settled.  The  former  seems  to  be  the  origin  of  that 
of  the  retinal  cells  and  probably  of  that  of  the  skin.  Recently  it  has 
been  found  that  the  pigment  is  of  nuclear  origin.  This  pyrenoid 
substance  arises  in  the  nucleus,  passes  through  the  nuclear  membrane 
into  the  cytoplasm  and  here  differentiates  into  melanin.  It  seems  to 
be  the  result  of  the  action  of  tyro  sin,  or  chromogen  of  the  cytoplasm, 
upon  the  tyrosinase  formed  by  the  nucleus. 

The  presence  of  pigment  in  the  skin  seems  to  be  for  the  purpose 
of  protection  against  the  actinic  rays  of  the  sun.  In  the  torrid 
regions  where  the  actinic  rays  are  most  active  Caucasians  who  are 
exposed  to  these  rays  very  much  soon  become  colored  or  tanned 
so  that  the  exposed  parts  of  the  body  no  longer  seem  to  belong  to  a 
Caucasian.     This  process  occurs   to  exposed  individuals  even  in 

27 


41 8  PRACTICAL   HISTOLOGY 

the  temperate  regions,  but  to  a  lesser  degree  as  the  actinic  rays 
here  are  not  so  powerful. 

The  skin  is  the  protective  organ,  and  varies  in  thickness  in  the 
different  regions.  It  is  thinner  on  the  less  exposed  surfaces,  as 
the  inner  surfaces  of  the  thighs  and  arms,  and  thicker  on  the  exposed 
regions,  as  back,  sole  and  palm. 

Upon  the  palmar  and  plantar  surfaces  the  epithelium  is  thrown 
into  ridges.  These  are  arranged  in  definite  patterns  characteristic 
of  each  individual.  Recorded  impressions  of  these  surfaces  have 
been  used  as  means  of  indentification  for  various  purposes.  Wilder 
considers  the  plantar  patterns  more  characteristic  than  the  palmar 
patterns. 

These  start  to  form  in  the  eleventh  week  of  intrauterine  life  and 
by  the  eighteenth  week  are  visible  upon  the  surface.  These  peculiar 
patterns  remain  permanent  throughout  life.  Even  though  the  epi- 
dermal surface  may  wear  somewhat  and  scars  may  be  present  the 
general  and  special  characteristics  may  still  be  made  out  as  Galton 
has  shown.  These  markings  are  present  even  in  the  skin  of  mum- 
mies and  also  in  specimens  preserved  in  jars.  Under  these  extreme 
conditions  they  are  still  clear  and  distinct.  Finger  prints  are  "now 
added  to  the  Bertillon  measurements  in  the  criminal  departments 
of  all  of  the  large  cities  and  they  have  proved  their  value. 

The  blood-vessels  of  the  skin  vary  in  size  and  number,  according 
to  the  location;  in  the  gluteal,  plantar  and  palmar  regions,  they  are 
greater,  while  in  the  most  movable  parts  they  are  most  branched. 
The  larger  trunks  lie  in  the  lower  part  of  the  corium  and  form  a 
plexus  parallel  to  the  surface.  This  plexus  supplies  the  fat  and 
sweat  glands.  Other  branches  pass  to  the  superficial  part  of  the 
corium,  anastomose  and  send  terminal  twigs  to  the  vascular  papillae 
{sub papillary  plexus)  and  to  the  hair  sheaths  and  sebaceous  glands. 
The  hair  papillae  receive  independent  branches.  In  the  papillae 
the  vessels  continue  as  venous  capillaries,  that  form  a  plexus  just  be- 
neath the  papillae  {sub papillary  plexus).  This  empties  into  another 
in  the  lower  portion  of  the  derma  that  cummunicates  with  a  sub- 
dermal  plexus;  the  latter  lies  between  the  derma  and  the  panniculus 
adiposus,  and  its  vessels  possess  valves. 

The  lymphatics  of  the  skin  consist  of  superficial,  or  papillary 


THE   SKIN   AND   ITS   APPENDAGES  419 

plexus,  which  receives  the  lymph  from  the  spaces  in  the  papillae, 
and  a  deeper,  or  subcutaneous  plexus  that  consists  of  larger  trunks, 
that  anastomose  with  the  above,  and  communicate  with  the  special 
plexuses  of  the  appendages. 

The  long  nerve  trunks  are  found  in  the  reticulare,  and  from  these 
branches  form  a  sub  papillary  plexus.  Myelinated  fibers  extend 
toward  the  surface,  and  form  the  special  organs. 

The  sensor  organs  are  very  numerous  in  the  skin.  These  comprise 
the  free  terminals,  or  those  in  which  the  naked  axis  cylinder  pierce 
the  epithelial  layer,  branch  and  send  these  divisions  between  epithelial 
cells.  The  higher  forms  of  beginnings  comprise  tactile  corpuscles  of 
Meissner,  most  numerous  in  the  palmar  and  plantar  skin  of  the  fingers 
and  toes  (there  is  usually  one  corpuscle  to  every  four  papillae;  here 
a  pad  of  tissue  is  found  that  corresponds  to  the  "walking  pads" 
of  carnivors);  bulbs  of  the  conjunctiva  and  genitalia;  Pacinian  bodies 
especially  in  the  palms  and  soles;  and  the  organs  of  Ruffini,  resem- 
bling the  neuro-muscular  organs.  For  a  detailed  description,  see 
Nerve  Tissue  (p.  156).  In  addition,  there  is  the  usual  nerve  supply 
to  the  blood-vessels. 

THE  APPENDAGES 

The  appendages  of  the  skin  are  the  hairs,  nails,  sebaceous, 
sweat  and  mammary  glands.  These  are  all  derived  from  the 
epidermis. 

THE  HAIRS 

The  hairs  are  protective  organs  limited  to  certain  portions  of 
the  body.  Hairs  are  absent  in  the  sole,  palm,  glans  penis,  glans 
clitoris,  prepuce,  medial  surfaces  of  the  labia  majora,  lateral  and 
palmar  surfaces  of  the  phalanges  and  the  dorsum  of  all  of  the  ungual 
phalanges.  They  are  most  numerous  upon  the  scalp  where  they 
average  from  200  to  300  per  square  centimeter.  Here  they  are 
distributed  in  groups  of  three  or  five.  The  slope  of  the  hair  varies 
in  different  parts  of  the  body.  They  seem  to  be  arranged  in  lines 
that  form  whorls,  making  a  general  hair  pattern  over  the  body 
surface.  Each  consists  of  a  root,  that  portion  within  the  skin,  and 
a  shaft,  that  part  seen  above  the  surface. 

The  root  is  somewhat  flask-shaped,  the  lower  end  being  enlarged 


420 


PRACTICAL   HISTOLOGY 


to  form  the  hair -bulb.  This,  on  its  under  surface,  is  indented  and 
invaginated  by  a  little  mass  of  connective  tissue,  the  hair  papilla, 
that  contains  a  small  tuft  of  capillaries,  upon  which  the  nourish- 


Shaft  of  a  hair. 
Stratum  corneum. 


Stratum  germinativum.  — JB 


Corium.— 5*ta 


Sebaceous  gland. -M 


M.  arrector  pili. 

Sweat  gland. 

Outer  epithelial  sheath. 


Inner  epithelial  sheath. — -H 
Medulla. — "3 


Cor 


Conn,  tissue  sheath. ,    J 


Bulb. fsr- 

Papilla.  """Stf 


Stratum  subcutaneum.  *""""fi| 
Epicranial  tendon  — -S 


***r»sL*eu 


Fig.  239. — Thick  Section  of  the  Human  Scalp.    X  20.    (Lewis  and  Stohr.) 

ment  of  the  hair  solely  depends.  The  root  is  surrounded  by  a 
condensation  of  the  derma,  in  which  the  connective  tissue  bundles 
are  arranged  into  two  layers. 


THE    SKIN   AND   ITS   APPENDAGES 


421 


In  the  outer,  the  fibers  have  a  longitudinal  course,  while  in  the 
inner,  they  run  circularly.  The  fibers  of  the  outer  layer  interlace 
somewhat  and  are  coarser  than  those  of  the  inner  layer.  Capillaries 
and  nerves  are  numerous  but  elastic  fibers  are  few  in  number.  The 
fibers  of  the  inner  layer  also  interlace  to  some  extent  and  contain  a 
rich  capillary  meshwork  and  many  nerve  fibers  that  form  a  plexus 
just  beneath  the  epithelial  layer.     Within  this  circular  layer  is  a 


Fig.  240. — From  a  Section  of  Scalp.     (Stohr's  Histology.) 
1,  Hair-shaft;  2,  hair-root;  3,  sebaceous  gland;  4,  arrector  pili  muscle;  5,  root 
sheaths;  6,  follicular  sheath;  7,  hair-bulb;  8,  papilla;  9,  fat  cells. 

prominent  homogeneous  band,  the  glassy  membrane.  This  repre- 
sents a  greatly  hypertrophied  basement  membrane.  It  is  partly 
derived  from  connective  tissue  and  partly  from  the  exoplasm  of 
the  epithelial  cells.  Few  connective  tissue  cells  are  present.  These 
layers  constitute  the  follicular  sheath.  Internal  to  it  are  found 
the  epithelial  cells,  which  are  continuous  with  the  epidermis.  These 
are  arranged  into  layers  that  are  the  root  sheaths,  of  which  there 
are  two,  outer  and  inner. 


422 


PRACTICAL  HISTOLOGY 


The  outer  root  sheath  is  the  direct  continuation  of  the  stratum 
Malpighii.     These  cells  are  the  same  as  elsewhere,  and  continue  to 

Hair  cuticle. 


TCorticle  substance  \   Sv,oft  ^f  +u*  i—  :- 

\  Medullary  substance  J    haft  of  the  hair 


Longitudinal  fibe 
layer 


Circular  fiber  layer 


Outer  layer  of  the 
hyaline  membrane 


Inner  layer  of  the 
hyaline  membrane 

Outer  epithelial 
sheath 


Henle's  layer 
Huxley's  layer 


Cuticle  of  the 
inner  sheath 


Papilla 


Fig.  241 . — Longitudinal  Section  of  the  Lowest  Part  of  the  Root  of  a  Hair. 
From  a  section  of  the  human  scalp.     (Lewis  and  Stohr.) 

the  bottom  of  the  root,  where  they  blend  with  those  of  the  inner 
root  sheath.     Throughout  the  greater  part  of  the  follicle,  this  layer 


THE    SKIN    AND    ITS    APPENDAGES 


423 


consists  of  several  rows  of  cells.     Toward  the  bulb,  it  gradually 
becomes  reduced  to  a  single  layer. 

The  inner  root  sheath  begins  at  the  lower  edge  of  the  orifice  of 
the  sebaceous  gland  that  opens  into  the  hair  follicle.  Above  the 
duct  it  is  replaced  by  the  stratum  corneum.  This  sheath  consists 
of  two  portions,  the  outer  of  which  is  called  the  layer  of  Henle. 
This  lies  next  to  the  outer  root  sheath,  and  is  composed  of  a  single 
layer  of  flattened  cells.     The  cells  are  clear  and  the  nuclei  are  usually 


Connective 
tissue  sheath.     ] 


Inner  epithelial 
sheath. 


Longitudinal  fiber 
layer. 
Circular  fiber 
layer. 


Hyaline  membrane 
Outer  epithelial  sheath. 
Henle's  layer. 


Huxley's  layer. 


Hair. 


Sheath  and  hair    cuti- 
cle. 
Cortical  substance. 


Medullary  substance. 


Fig.  242. — From  a  Horizontal  Section  of  the  Human  Scalp. 

X  240.    (Stohr.) 
Cross-section  of  a  hair  and  its  sheaths  in  the  lower  half  of  the  root. 


invisible.  This  layer  is  comparable  to  the  stratum  lucidum  of  the 
skin  and  may  be  absent  or  seem  a  part  of  the  inner  root  sheath. 
Within  this  layer  is  the  sheath,  or  layer  of  Huxley,  which  consists 
of  two  or  three  layers  of  large  irregular  cells.  The  cells  are  flattened 
and  keratinized  and  correspond  to  the  cells  of  the  stratum  corneum 
of  the  epidermis.  It  must  be  borne  in  mind  that  the  structure  of 
the  root  varies  at  different  levels  and  in  order  to  see  all  of  the  men- 
tioned layers  the  section  must  be  some  distance  from  the  bulb.  In 
the  bulb  the  root  sheaths  are  no  longer  distinguishable  as  distinct 


424  PRACTICAL   HISTOLOGY 

and  separable  layers  but  blend.  Most  of  the  cells  represent  the 
outer  root  sheaths  which  are  the  elements  that  really  form  the  hair. 
Their  great  number  cause  the  formation  of  the  bulbous  portion  of 
the  root.  The  cells  here  may  often  contain  a  large  number  of  pig- 
ment granules. 

The  hair  papilla  is  a  club-shaped  mass  of  delicate  connective 
tissue  from  the  derma  in  which  the  connective-tissue  cells  are  very 
numerous.  It  contains  a  rich  plexus  of  blood  capillaries  and  also 
many  nerve  fibers  that  are  no  doubt  trophic  in  function. 

The  hair  occupies  the  central  portion  of  the  follicle,  and  is  com- 
posed of  three  parts,  cuticle,  cortex  and  medulla. 

The  cuticle  is  composed  of  a  single  layer  of  irregular,  nonnucleated 
scales.  These  are  very  thin  and  overlap.  Within  the  follicle  they 
he  closely  applied  to  the  layer  of  Huxley.  These  cells  are  thin  and 
keratinized.  The  cortex  consists  of  a  great  many  layers  of  long, 
spindle-shaped  elements.  The  nuclei  are  rod-shaped.  These  cells 
are  keratinized  and  may  contain  pigment  granules. 

The  medulla  is  absent  in  lanugo  hairs  and  usually  so  in  the  hairs 
of  the  scalp.  The  medulla,  when  present,  is  composed  of  several 
rows  of  cuboidal  cells  that  do  not  extend  the  length  of  the  hair. 
They  contain  granules  of  keratohyalin,  and  frequently  have  a  dark 
appearance;  this  is  due  to  the  presence  of  small  air-bubbles. 

The  heaviest  hairs  are  found  on  the  scalp  and  pubis,  in  the  axilla, 
and  upon  the  face  of  males.  Those  of  the  scalp  measure  from  n  to 
1 60  microns  and  those  of  the  face  up  to  200  microns  in  diameter. 
Delicate  hairs  occur  all  over  the  body  surface  and  measure  about  5 
microns  in  diameter;  these  are  like  the  lanugo  hairs  of  the  fetus. 

Light-colored  hairs  are  finer  than  black  hairs.  The  straight  hairs 
are  usually  coarser  and  thicker  than  the  crisp  hairs  and  on  cross- 
section  are  usually  circular  in  outline.  The  crisp  hairs  are  oval 
upon  section  and  are  most  flattened  in  the  Japanese,  Chinese  and 
Indians. 

Shortly  before  and  after  birth  there  is  a  general  shedding  of  the 
hairs.  In  adults  this  loss  and  renewal  is  constant.  Scalp  hairs 
are  said  to  live  1600  days.  The  process  of  shedding  is  as  follows: 
The  hyalin  membrane  and  circular  fibers  of  the  outer  root  sheath 
thicken,  and  the  matrix  ceases  to  produce  an  inner  root  sheath. 


THE    SKIN   AND   ITS   APPENDAGES 


425 


The  bulb  becomes  cornified  and  frayed.  The  increase  of  undif- 
ferentiated cells  forces  the  old  hair  and  inner  root  sheath  outward. 
The  hair  follicle  collapses  and  shortens.  Later  the  matrix  cells 
proliferate,  lengthen  the  follicle  and  produce  a  new  hair. 

The  color  of  the  hair  is  due  to  pigment  granules  in  the  cortex. 
These  cells  may  even  contain  pigment  in  solution.  Diffuse  pigment 
is  abundant  in  dark  and  red  hairs,  but  absent  in  white. 


Fig.  243. — Longitudinal  Section  of  Hair  Follicles  in  the  Scalp  of  a  Fetus. 

a,   Papilla;     b,   Epithelial  root  sheaths;     c,  shaft;     d,  sweat-gland. 

(Photograph.     Obj.  16  mm.,  oc.      10  X.) 

Opening  into  the  hair  follicles  are  the  sebaceous  glands.  This 
is  usually  upon  the  side  toward  which  the  hair  leans,  and  here  is  also 
seen  the  muscle  of  the  hair  follicle,  the  arrector  pili  muscle.  This  is 
smooth  muscle,  and  is  attached  above  to  the  derma,  just  beneath  the 
stratum  Malpighii,  and  below  to  the  hair  bulb.     When  it  contracts  it 


426  PRACTICAL   HISTOLOGY 

causes  the  hair  to  " stand  on  end.'"  Arrector  pili  muscles  are  absent 
in  hairs  of  the  cheeks  and  lips  and  of  the  hairs  of  the  eyelids  (lashes) 
and  of  the  nasal  fossae  (vibrissas). 

The  blood-supply  of  the  hair  is  a  special  vessel  that  passes  to  the 
bulb  and  in  the  papilla,  forms  a  tuft  of  capillaries  and  upon  this 
the  nourishment  of  the  hair  depends.  The  venous  blood  is  returned 
to  the  general  cutaneous  plexus  of  the  neighborhood. 

Each  hair  receives  nerve  fibers  for  the  papilla,  follicle  and  arrector 
muscle.  That  for  the  follicle  divides  into  branches  that  encircle 
the  follicle  and  terminate  between  the  epithelial  cells  of  the  root 
sheaths.  That  for  the  papilla  forms  a  series  of  fine  branches  in  the 
papillary  connective  tissue.  The  nerve  fiber  for  the  muscle  is  from 
the  sympathetic  system. 

THE  NAILS 

The  nails  are  peculiar  appendages  that  serve  for  the  protection 
of  the  ends  of  the  fingers  and  toes,  and  consist  of  the  root  and  the 
nail-body. 

The  root  is  the  proximal  end  at  which  the  organ  grows.  Here 
the  epithelial  cells  are  transformed  into  the  hard  substance  that 
gives  the  nail  its  character.  Along  the  sides,  the  nail  is  protected 
by  an  overhanging  ledge  of  skin,  which  constitutes,  at  the  root,  the 
nail-fold,  and  at  the  sides,  the  nail-wall.  The  angle  formed  by  the 
nail  and  wall  is  the  nail-groove.  The  stratum  corneum  continues 
into  the  angle  over  the  edge  of  the  nail  as  the  eponychium. 

The  nail-body  consists  of  the  nail  proper  and  the  nail-bed  upon 
which  the  nail  rests. 

The  nail  represents  a  greatly  hypertrophied  stratum  lueidum.  The 
cells  are  flattened  elements,  in  which  the  nuclei  are  indistinct,  and 
the  cytoplasm  clear.  At  the  proximal  end  is  the  root,  and  at  this 
place  alone  the  nail  grows.  It  is  marked  by  a  white  area,  the  lunula. 
Here  the  epithelial  layer  is  so  thick  that  the  underlying  capillaries 
are  invisible  according  to  some.  According  to  others  the  color  is 
due  to  the  presence  of  keratohyalin  granules  in  the  cells.  Still  others 
believe  that  the  light  area  is  caused  by  the  separation  of  the  nail  from 
the  bed  in  this  area.     The  cells  also  are  said  to  contain  keratohyalin 


THE    SKIN    AND    ITS    APPENDAGES 


427 


granules.  At  the  distal  end,  the  nail  projects  as  the  free  edge, 
which  is  produced  by  a  forward  growth  due  to  the  formation  of  new 
cells  at  the  root  area.  The  nail  is  derived  from  the  cells  of  the 
stratum  Malpighii  of  the  root  region.  These  new  cells  pass  toward 
the  surface,  the  cytoplasm  becomes  permeated  with  eleidin  and  the 
nucleus  all  but  disappears.  The  result  is  the  formation  of  a  thick 
stratum  lucidum  that  represents  the  nail.  Nothing  is  added  to  the 
nail  beyond  the  root  area.  From  the  root  the  nail  is  carried  over  the 
bed  to  the  free  edge  at  the  rate  of  about  0.75  mm.  per  week. 

The  nail  bed  consists  of  the  stratum  Malpighii  and  the  corium. 
The  stratum  Malpighii  resembles  that  of  the  skin  surface,  and  rests 


Fig.  244. — Cross-section  of  Nail. 

1,  Nail;  2,  corium;  3,  epithelium;  4,  nail-wall;  5,  nail-groove;  6,  bone  of  phalanx; 

7,  eponychium. 


upon  the  papillated  corium.  That  portion  beneath  the  lunula  is 
termed  the  matrix.  The  corium  is  composed  of  bundles  of  white 
fibrous  and  yellow  elastic  tissues  that  have  a  general  longitudinal 
direction.  Between  the  bundles  are  vertical  fibers  that  pass  from 
the  periosteum  toward  the  nail.  The  papillae  of  the  bed  are  not 
like  those  of  the  skin,  but  consist  of  long  ridges  that  extend  from  the 
root  to  the  end  of  the  nail.  They  are  small  beneath  the  root,  but 
increase  in  height  as  the  free  edge  is  approached,  and  end  abruptly 
at  that  point.     The  nail  bed  is  very  vascular. 

The  nails  represent  protective  structures.  In  some  of  the  lower 
animals  they  take  the  form  of  claws  where  they  represent  weapons 
of  offense"and  defense.     In  still  other  forms  they  become  markedly 


428  PRACTICAL   HISTOLOGY 

hypertrophied  and  extended  so  that  the  animal  walks  upon  them, 
constituting  their  hoofs.  In  some  animals,  as  the  elephant,  the  nails 
are  extremely  sensitive. 

THE   GLANDS 

The  glands  comprise  the  sweat,  sebaceous  and  mammary  glands. 

The  sudoriferous  or  sweat-glands  are  of  the  coiled  tubular  variety. 
Each  consists  of  a  secretory  portion,  3  mm.  long,  three-fourths  of 
which  constitutes  the  coil  that  lies  in  the  stratum  reticulare,  and  an 
excretory  duct  that  passes  up  through  the  derma  and  cuticle  to  open 
upon  the  surface. 

The  secretory  portion  consists  of  a  single  layer  of  cuboidal  cells 
lining  the  tub  ale.  These  are  separated  from  the  basement  membrane 
by  a  layer  of  smooth  muscle  fibers.  This  is  wanting  in  the  smallest 
sweat-glands  and  is  best  developed  in  those  of  the  axilla,  labia 
majora,  root  of  the  penis  and  circumanal  region. 

The  cytoplasm  is  granular  and  may  contain  pigment  granules 
and  fat  globules.  There  are  said  to  be  two  varieties  of  cells  present, 
one  that  is  clear  and  the  other  that  is  dark  and  granular.  During 
the  period  of  rest  the  cells  are  taller  and  clear  and  intracellular  and 
intercellular  canaliculi  are  noted.  The  lumen  of  the  tubule  may 
be  almost  occluded.  During  the  stage  of  secretory  activity  the 
secretion  is  poured  into  the  lumen  by  way  of  the  canaliculi,  the  cells 
are  small  and  shrunken  and  the  cytoplasm  has  a  granular  appearance. 
Delicate  rods  may  be  seen  in  the  basal  portions  of  the  cells.  The 
nucleus  is  usually  quite  distinct.  The  secretory  tubule  is  coiled 
upon  itself,  and  the  various  convolutions  are  separated  from  one 
another  by  interstitial  tissue  that  corresponds  to  the  tunica  propria. 
The  secretion  is  eliminated  from  the  cells  by  inter-  and  intracellular 
capillaries. 

The  duct  that  leads  from  the  secretory  part  to  the  surface  has 
usually  one-half  the  diameter  of  the  secretory  tubule,  and  is  lined 
by  two  layers  of  cells  that  rest  upon  a  basement  membrane  and  tunica 
propria  but  muscle  tissue  is  absent.  In  the  epidermis  its  course  is 
spiral,  and  no  separate  wall  is  present,  the  epithelial  cells  of  the 
epidermis  acting  in  this  capacity.  The  diameter  of  this  portion  is 
greater  than  that  of  the  corium.     Its  opening  upon  the  surface  is 


THE    SKIN   AND   ITS   APPENDAGES  429 

large  and  trumpet-shaped,  visible  to  the  naked  eye  and  is  called  the 
sweat-pore. 

These  glands  are  generally  distributed,  except  on  the  margins  of  the 
lips,  glans  penis  and  inner  surface  of  the  prepuce.  They  are  most 
numerous  in  regions  devoid  of  hairs  as  the  palm,  where  they  number 
about  370  per  square  centimeter;  they  are  largest  in  the  axilla. 
Upon  the  breast  and  abdomen  there  are  about  155  per  square 
centimeter  while  upon  the  limbs,  neck  and  trunk  there  are  about 
60  to  80  per  square  centimeter. 

The  average  diameter  is  1  mm.,  but  in  the  axillary  region  they  may 
attain  a  size  of  3  or  4  mm.  comprising  30  to  40  mm.  of  coiled  tube. 
In  this  region  the  secretory  tubule  may  be  branched.  They  acquire 
their  large  size  at  puberty,  and  have  been  termed  sexual  odoriferous 
glands.  In  the  anal  region  the  sweat-glands  are  mainly  branched. 
Some  of  the  large  unbranched  glands  here  are  called  circumanal 
glands. 

The  normal  secretion  is  a  thin  watery  fluid  called  perspiration. 
This  represents  an  excretion  and  besides  sodium  chlorid  contains  a 
small  amount  of  urea.  These  glands  are,  in  a  way,  accessories  to 
the  kidneys  and  in  certain  diseases  of  the  kidneys  the  sweat  glands 
will  excrete  an  increased  quantity  of  urea.  In  addition  to  this  func- 
tion the  sweat  glands  are  important  in  maintaining  an  even  body 
temperature.  When  the  external  temperature  runs  high  the  skin 
temperature  tends  to  do  the  same  but  the  sweat  glands  pour  out 
their  fluid  and  through  the  evaporation  of  this  the  temperature  is 
held  down.  When  the  humidity  and  temperature  are  high,  or 
during  heavy  exercise  even  in  moderate  weather  the  effort  of  these 
glands  to  maintain  an  even  temperature  of  the  body  is  seen  in  the 
great  amount  of  perspiration  formed.  As  the  quantity  formed  is  too 
great  to  be  evaporated  the  excess  runs  off  in  streams. 

The  ceruminous  glands  of  the  eyelids,  and  of  the  external  auditory 
canals  and  the  circumanal  glands  are  modified  sweat  glands.  The 
secretion,  however,  is  of  a  fatty  nature  but  the  general  structure  is 
the  same.  The  glands  of  Moll  of  the  eyelids  and  the  circumanal 
glands  are  usually  of  the  branched  type. 

The  sebaceous  glands  are  racemose  structures.  They  vary  in 
size  from  0.2  to  2.2  mm.     They  are  usually  found  in  connection 


430 


PRACTICAL  HISTOLOGY 


with  the  hair  follicles;  the  largest  hairs  possess  small  glands,  while 
the  smallest  hairs  are  appendages  of  the  attached  sebaceous  glands. 
The  largest  glands  are  found  on  the  nose  where  the  ducts  are  visible 
to  the  naked  eye.  Each  is  surrounded  by  a  capsule  of  white  fibrous 
tissue  that  forms  the  supportive  structure. 

The  alveoli  are  from  4  or  5  to  20  in  number  and  are  lined  by  cells 
that  are  a  continuation  of  the  cells  of  the  stratum  Malpighii,  and 
which  rests  upon  a  basement  membrane  and  tunica  propria.     The 


Fig.  245. — Section  of  Three  Alveoli  of  a  Sebaceous  Gland  showing  Their 
Solid  Structure.     (Photograph.     Obj.  16  mm.,  oc.  10  X.) 

basal  cells  are  small,  while  larger,  rounded  cells  in  various  stages  of 
fatty  change  completely  fill  the  alveolus.  Those  in  the  center,  where 
the  lumen  should  be,  are  further  advanced  in  changes  than  the  basal 
cells.  The  entire  cytoplasm  becomes  converted  into  oil,  which 
constitutes  the  secretion,  and  is  called  sebum;  the  nucleus  likewise 
degenerates.  The  sebum  is  semi-fluid  and  consists  of  fat  and  dis- 
integrated cells.  The  death  of  the  cell  is  necessary  to  the  formation 
of  this  secretion.  The  transformed  cell  is  immediately  replaced  by 
another.  The  excretory  duct  is  lined  by  several  layers  of  cells  that 
do  not  take  part  in  the  secretory  activity,  and  are  derived  from  the 
outer  root  sheath  of  the  hair  follicle. 

Sebaceous  glands  are  found  in  some  regions  devoid  of  hairs,  as 


THE    SKIN   AND   ITS   APPENDAGES  43 1 

in  the  margins  of  the  lips,  glans  penis,  prepuce,  glans  clitoris  and  labia 
minora.     None  are  found  in  the  palms  and  soles. 

THE  MAMMARY  GLAND 

The  mammary  gland  is  a  multiple  alveolo-tubular  organ.  Accord- 
ing to  some  writers,  it  is  a  modified  sweat  gland,  while  others  hold 
it  to  be  a  modified  sebaceous  structure.  It  is  composed  of  from  fifteen 
to  twenty  individual  compound  glands.  Each  of  these  possesses  its 
own  excretory  duct,  that  has  its  own  opening  in  the  nipple.  The 
entire  organ  is  covered  by  skin.  This  gland  grows  somewhat  in 
both  sexes  until  puberty.  Then  in  the  male  all  but  the  main  ducts 
atrophy. 

Each  gland  consists  of  lobes  and  lobules  separated  and  supported 
by  white  fibrous  and  adipose  tissues.  All  of  the  individual  glands 
are  further  bound  together  in  the  same  manner.  The  ducts  con- 
verge and  end  in  the  nipple,  which  forms  a  small  projecting  mass. 

Each  lobule  consists  of  a  number  of  acini,  which  are  tubular  or 
alveolar  in  structure.  The  number  of  these  depends  upon  the  state 
of  activity.  In  the  gland  of  pregnancy,  the  acini  are  very  numerous, 
and  are  lined  by  simple  columnar,  or  cuboidal  cells,  in  which  are 
accumulated  the  fat  globules  that  form  the  important  constituent 
of  the  milk.  These  cells  rest  upon  a  basement  membrane,  but  in 
places  are  separated  therefrom  by  peculiar  elements  called  basket 
cells,  which  are  compared  to  the  smooth  muscle  tissue  of  the  sweat 
glands.  The  ducts  are  lined  by  simple  columnar  cells  that  rest  upon 
a  basement  membrane,  outside  of  which  circular  bundles  of  white 
fibrous  tissue  are  to  be  found.  These  ducts  unite  to  form  the  main 
secretory  duct  of  the  individual  glands;  each  main  duct  dilates  to  form 
a  small  ampulla,  or  sinus  lactiferous,  before  the  nipple  is  reached. 

The  nonlactating  gland  consists  chiefly  of  white  fibrous  and  adipose 
tissues,  in  which  are  seen  a  number  of  ducts,  but  few  acini.  The 
bulk  of  the  organ  consists  of  the  fibrous  and  adipose  tissues.  When 
pregnancy  occurs,  the  ducts  divide  and  redivide,  and  the  terminal 
portions  dilate  to  form  the  acini.  This  increase  in  the  glandular 
part  causes  the  increase  in  the  size  of  the  organ,  and  the  tingling 
sensation  that  occurs  at  that  time. 

After  lactation  has  ceased,  most  of  the  acini  undergo  retrogression, 


43  2 


PRACTICAL  HISTOLOGY 


atrophy,  and  disappear.  Some  of  the  ducts  undergo  the  same 
change.  As  a  result,  the  gland  becomes  somewhat  smaller  and 
flabby.  In  old  age,  or  after  the  child-bearing  period  has  passed, 
the  glandular  and  ductular  portions  retrograde  and  disappear  in  the 
same  manner,  until  in  old  age,  they  may  be  entirely  absent.  The 
glands  are  then  represented  by  fibrous  and  adipose  tissues. 


Branch  of  an  excretory  duct. 


Connective  tissue. 


Tubule. 


Alveolo-tubular 
end  piece. 


Fig.  246. — Section  ofLactating  Human*  Mammary  Gland.   (Stdhr's  Histology.) 

Milk  consists  of  minute  globules  of  fat,  0.1  to  0.5  mm.  in  diameter, 
surrounded  by  a  thin  layer  of  casein.  This  prevents  them  from 
coalescing.  They  are  formed  in  the  cytoplasm  of  the  cells  of  the 
acini,  but  the  cell,  after  discharging  them,  does  not  die,  as  formerly 
supposed.  At  first  colostrum  is  present  in  the  glands;  this  consists 
of  fat  and  colostrum  corpuscles,  which  are  either  degenerated  gland 
cells,  or  leukocytes. 

The  nipple,  or  mammila,  consists  of  an  outer  covering  of  pigmented 
skin,  and  within  it  the  individual  ducts  are  found.    These  are  sepa- 


THE    SKIN    AND   ITS   APPENDAGES  433 

rated  from  one  another  by  fibrous  tissue  and  involuntary,  non- 
striated  muscle.  The  muscle  tissue  is  arranged  circularly  and  ver- 
tically, extending  to  the  apex  of  the  mammila.  By  its  contraction, 
an  erection  is  produced.  Such  tissue  is  called  false  erectile  tissue. 
At  the  base  of  the  nipple  is  a  pigmented  area  called  the  areola,  which 
contains  a  ring  of  branched  tubular  glands  called  the  glands  of 
Montgomery.  These  resemble  the  mammary  gland  and  are  regarded 
as  transitional  forms  between  the  sweat  and  mammary  glands. 
Occasionally  rudimentary  hairs  are  found  in  the  areola. 

In  addition  to  the  general  blood-vessels,  the  various  appendages 
have  special  supplies.  From  the  sub  papillary  arterial  plexus, 
branches  pass  to  the  hair  follicles,  to  form  one  plexus  beneath  the 
hyalin  membrane,  and  another  in  the  papilla.  The  venous  radicals 
formed,  empty  into  subpapillary  plexus  of  veins.  Around  the  se- 
baceous and  sweat  glands,  the  subpapillary  arterial  plexus  forms  a 
close  network  of  capillaries  which  form  venous  branches  that  empty 
into  the  subpapillary  venous  plexus. 

The  blood-vessels  of  the  mammary  gland  converge  toward  it,  and 
pass  into  the  organ  in  the  partitions  between  the  lobules.  From 
these  vessels,  branches  extend  into  the  lobules,  and  form  close  plex- 
uses around  the  acini. 

The  appendages  are  supplied  with  nerves-  from  both  sympathetic 
and  cerebrospinal  systems.  The  hair  follicles  receive  myelinated 
fibers  that  branch  freely,  and  end  in  spoon-shaped  masses  upon  the 
glassy  membrane.  The  sweat  glands  are  supplied  with  sympathetic 
fibers,  that  form  a  close  network  beneath  the  basement  membrane, 
which  they  pierce,  to  end  upon  the  gland  cells.  The  mammary 
gland  has  both  varieties  of  nerves.  The  sympathetic  are  the  more 
numerous;  these  pass  to  the  blood-vessels  on  the  one  hand,  and  to 
the  acini  on  the  other.  In  the  latter,  they  form  a  plexus  beneath 
the  basement  membrane,  and  from  this  plexus,  branches  end  upon 
the  gland  cells.     The  nerve  beginnings  in  the  nipple  are  numerous. 

The  glands  and  hair  follicles  are  surrounded  by  separate  lymphatic 
plexuses  that  empty  into  the  subcutaneous  vessels.  In  the  mam- 
mary gland,  plexuses  are  found  between  the  individual  lobes,  around 
the  ampullae  and  in  the  nipple.  These  empty  into  the  axillary 
lymph  nodes. 

28 


CHAPTER  XVII 
THE  NERVE  SYSTEM 

The  nerve  system  comprises  two  main  divisions,  the  central  and 
the  peripheral.  The  central  division  consists  of  the  cerebrum, 
cerebellum,  pons,  oblongata  and  spinal  cord;  the  peripheral  portion 
consists  of  the  cerebral  and  spinal  nerves  and  their  connected  ganglia. 
The  central  portions  are  surrounded  by  three  membranes,  the 
dura,  the  arachnoid  and  the  pia. 

The  dura  is  a  tough  membrane  composed  of  interlacing  bundles 
of  white  fibrous  and  yellow  elastic  tissues  that  contain  lymph  spaces 
between  them.  Sensor  nerves  are  numerous.  Within  the  skull  the 
dura  comprises  an  outer  part  that  is  the  periosteum  of  the  bones  of 
the  skull  and  this  is  quite  vascular;  the  inner  portion  is  tougher  and 
denser  and  less  vascular  and  represents  the  real  covering  of  the  brain. 
It  continues  in  between  the  two  hemicerebri  to  form  the  falx  cerebri, 
between  the  cerebrum  and  cerebellum  it  forms  the  tentorium  cerebelli; 
other  derivatives  are  the  falx  cerebelli  and  the  diaphragm  sella.  It 
also  forms  the  walls  of  the  great  venous  sinuses  of  the  skull  and  is 
continued  upon  the  roots  of  the  cerebral  nerves  for  a  short  distance. 
At  the  foramen  magnum  the  two  layers  become  permanently  and 
distinctly  separated  from  each  other,  so  that  within  the  vertebral 
canal  the  dura  hangs  like  a  bag  to  the  third  division  of  the  sacrum. 
Within  this  bag  is  the  spinal  cord.  Within  the  spinal  dura  the 
bundles  of  fibers  have  chiefly  a  longitudinal  direction. 

Within  the  cranial  cavity  the  internal  surface  of  the  dura  is  lined 
with  endothelial  cells  and  the  membrane  forms  the  outer  boundary 
of  the  subdural  lymph  space.  Within  the  vertebral  canal  both 
surfaces  of  the  dura  are  covered  with  endothelial  cells  and  the  space 
between  the  dura  and  the  bony  canal  is  the  epidural  lymph  space. 

The  epidural  lymph  space  is  not  a  simple  cavity  but  is  crossed  by 
trabecular  that  connect  the  two  layers  of  the  dura.     These  trabecular 

434 


THE    NERVE    SYSTEM  435 

are  covered  with  endothelial  cells.  Within  the  vertebral  canal  where 
the  two  layers  are  well  separated  these  trabecular  form  a  series  of 
large  and  extensive  lymph  spaces,  while  within  the  cranial  cavity, 
where  the  layers  are  close  together,  these  spaces  are  fewer  and  smaller. 
These  spaces  are  in  open  communication  and  continuous  with  the 
lymph  spaces  around  the  vessels  and  nerves  and  these  practically 
represent  efTerents  of  the  epidural  spaces. 

The  subdural  lymph  space  is  a  clear-cut  narrow  cavity  between 
the  dura  and  the  arachnoid.  It  is  bounded  by  the  endothelial  cells 
that  line  the  inner  surface  of  the  dura  and  cover  the  superficial  layer 
of  the  arachnoid.  As  the  membranes  of  the  brain  and  spinal  cord 
are  continued  upon  the  cerebral  and  spinal  nerves  for  a  short  dis- 
tance and  then  blend  with  the  epineurium  of  these  nerves  this 
lymph  space  extends  into  the  nerves  and  become  continuous  with 
the  perineural  lymph  spaces  that  represent  drainage  channels  for 
this  space. 

The  arachnoid  is  a  delicate,  web-like  membrane  that  is  composed 
of  loosely  interwoven  bundles  of  white  fibrous  tissue  and  a  few 
elastic  fibers;  it  is  said  to  be  devoid  of  vessels  and  nerves.  It  is 
closely  applied  to  the  pia  but  does  not  follow  it  into  the  fissures  and 
sulci  except  in  the  case  of  the  sagittal  and  lateral  cerebral  fissures. 
The  peripheral  surface  of  the  arachnoid  is  covered  with  endothelial 
cells  that  are  continuous  with  those  lining  the  deep  surface  of  the 
dura,  but  these  two  membrances  are  not  connected  to  each  other. 
The  deep  surface  of  the  arachnoid  is  also  covered  by  endothelial  cells. 
From  this  surface  numerous  bands  or  trabecular  pass  to  the  pia  so 
that  instead  of  a  clear-cut  space  between  these  two  membranes  a 
series  of  intercommunicating  spaces  is  formed  and  these  constitute 
the  subarachnoid  lymph  space.  The  trabecule  are  covered  with 
endothelial  cells  that  are  continuous  with  those  covering  the  pe- 
ripheral surface  of  the  pia.  This  space  does  not  communicate  with 
the  subdural  space.  The  arachnoid  forms  a  number  of  reddish- 
brown  structures  that  project  into  the  venous  sinuses.  These  are 
the  Pacchionian  bodies  (granulationes  arachnoideales)  and  although 
they  appear  to  lie  within  the  sinuses  they  are,  however,  covered  with 
a  thin  layer  of  dura.  Through  these  the  lymph  of  the  subarachnoid 
space  may  reach  the  venous  circulation.     In  certain  regions  the 


43  6  PRACTICAL  HISTOLOGY 

arachnoid  and  pia  are  separated  more  extensively  forming  spaces 
called  the  cisternce  subarachnoideales. 

The  subarachnoid  lymph  space  is  broader  in  the  vertebral  canal 
than  in  the  skull.  It  communicates  with  the  canal  of  the  spinal 
cord  and  ventricles  of  the  brain  through  the  foramen  in  the  dorsal 
wall  of  the  fourth  ventricle  and  through  the  lateral  apertures  of 
this  ventricle.  It  has  a  capacity  of  about  5  cu.  mm.  and  the  lymph 
present  constitutes  the  cerebrospinal  fluid. 

The  pia  is  the  vascular  membrane  of  the  brain  and  spinal  cord  as  it 
contains  all  of  the  arterial  vessels  and  some  of  the  smaller  venous 
channels.  It  is  closely  applied  to  the  surface  of  the  brain  and 
spinal  cord  and  enters  into  all  of  the  fissures  and  sulci,  more  so 
in  the  cerebrum  than  in  the  cerebellum.  It  consists  of  two  principal 
layers,  an  outer  in  which  the  fibers  are  longitudinal  in  the  vertebral 
canal  and  the  inner  ones  are  circularly  directed  there.  This  layer 
formation  is  not  so  distinct  in  the  pia  of  the  cranial  cavity  as  there 
is  a  tendency  for  the  fibers  to  interlace.  Between  these  two  layers 
are  the  blood-vessels  and  the  larger  ones  project  into  the  subar- 
achnoid space.  The  peripheral  surface  of  the  pia  is  covered  with 
endothelial  cells  that  represent  a  part  of  the  boundary  of  the  subar- 
achnoid space  and  are  continuous  with  those  of  the  deep  surface  of 
the  arachnoid.  This  surface  is  connected  to  the  arachnoid  by 
numerous  trabecular,  covered  with  endothelial  cells.  The  deep  sur- 
face of  the  pia  is  closely  applied  and  firmly  attached  to  the  surface  of 
the  brain  and  spinal  cord.  This  attachment  is  due  to  the  delicate 
trabecular  that  extend  into  the  nerve  tissue  accompanying  the  blood- 
vessels. In  this  deep  layer  are  the  smaller  blood-vessels  which  enter 
the  nerve  substance  from  the  outside. 

Some  sensor  fibers  are  present  in  the  pia  but  most  of  the  nerves 
are  of  the  sympathetic  system  and  pass  to  the  blood-vessels. 

The  nerve  system  is  made  up  of  two  kinds  of  nerve  tissue,  gray 
and  white.  The  gray  substance  is  characterized  by  a  grayish  color. 
In  the  cerebrum  and  cerebellum  it  is  generally  arranged  in  layers 
that  are  visible  only  under  the  microscope.  In  the  spinal  cordr 
brain  stem  and  ganglia  the  arrangement  is  different  as  will  be  pointed 
out  when  these  structures  are  considered. 
~Gray  nerve  tissue  consists  of  nerve  cells  and  their  processes,  myelin- 


mi;    NERVE    SYSTEM  437 

ated  and  a  myelinated  nerve  fibers  and  neuroglia,  the  special  sup- 
portive tissue  of  the  nerve  system.  The  white  substance  of  the 
central  nerve  system  consists  chiefly  of  myelinated  nerve  fibers, 
neuroglia  and  a  small  amount  of  white  fibrous  connective  tissue  that 
accompanies  the  blood-vessels  but  this  is  not  supportive  to  the 
neural  elements.  The  peripheral  system  consists  of  some  ganglia 
and  of  nerve  fibers,  the  latter  are  supported  mainly  by  white  fibrous 
tissue  that  form  the  sheaths  of  the  nerves.  This  portion  of  the 
nerve  system  has  been  considered  under  Nerve  Tissues. 

The  nerve  system  consists  of  a  series  of  inter-related  and  inter- 
connected units  that  give  a  continuity  of  impulse  from  the  central 
system  to  the  periphery  of  the  body  and  vice  versa.  These  units  are 
called  neurons;  each  neuron  consists  of  the  nerve  cell  and  its  various 
processes.  The  nerve  cell  comprises  the  cytom,  or  cell  body  and  the 
proximal  portions  of  the  dendritic  and  axonic  processes.  The 
distal  portion  of  the  axone  and  the  distal  portion  of  the  principal 
dendrite,  if  it  leaves  the  gray  substance  and  becomes  a  nerve  fiber 
as  in  the  sensor  system,  constitute  the  nerve  fibers.  These  fibers  may 
be  from  a  few  millimeters  to  several  feet  in  length. 

Nerve  cells  vary  in  size  and  shape  and  may  be  unipolar,  bipolar 
or  multipolar,  according  to  the  number  of  processes.  The  main 
process  is  the  axone,  the  others  are  the  dendrites.  If  the  axone 
leaves  the  gray  substance  the  cells  are  classed  as  a  cell  of  the  first 
type,  or  Deiter's  cell.  If  the  axone  remains  within  the  gray  substance 
the  cell  is. of  the  second  type,  or  Golgi  cell. 

The  neuroglia  consists  of  glial  cells  and  glial  fibers.  The  glial 
cells  comprise  ependymal  cells  and  astrocytes  of  the  spider  and  mossy 
types.  For  a  detailed  description  of  nerve  cells,  their  processes, 
neuroglia  and  nerve  fibers  see  Nerve  Tissues. 

In  the  cerebrum  and  cerebellum  the  gray  substance  is  externally 
placed  and  constitutes  the  cortex;  the  white  substance  is  internal, 
completely  covered  by  the  gray  and  is  called  the  medulla.  In  the 
spinal  cord  the  gray  substance  is  collected  into  a  characteristic  mass 
internally  and  completely  surrounded  by  the  white  substance.  In 
the  brain  stem  (oblongata,  pons  and  midbrain)  there  is  no  special 
arrangement  as  the  gray  and  white  are  more  or  less  intermingled 
with  each  other. 


38  PRACTICAL  HISTOLOGY 

THE  SPINAL  CORD 

The  spinal  cord  (medulla  spinalis)  the  longest  portion  of  the 
central  nerve  system  and  is  that  part  within  the  vertebral  column. 
It  is  suspended  in  the  vertebral  canal  and  is  covered  by  the  meninges 
of  which  the  dura  forms  a  bag.  It  is  considerably  smaller  than  the 
canal  in  diameter  so  that  movements  of  the  vertebrae  do  not  injure 
it  under  normal  conditions.  It  is  somewhat  cylindrical  in  shape  and 
extends  from  the  margin  of  the  foramen  magnum  to  the  lower  border 
of  the  first  or  upper  border  of  the  second  lumbar  vertebra.  In  the 
male  it  measures  about  45  cm.  and  in  the  female  about  43  cm.  in 
length.  Its  weight,  when  stripped,  is  about  30  grams  and  with  the 
nerve  roots  about  45  grams. 

This  portion  of  the  nerve  system  is  the  longest.  It  is  character- 
ized by  possessing  the  gray  substance  internally  and  the  white 
substance  externally.  Its  form  varies  in  the  different  regions; 
in  the  cervical  and  lumbar  areas,  it  is  enlarged,  and  these  enlarge- 
ments are  termed  the  intumescentiacervicalis  and  lumbalis,  respect- 
ively. The  cervical  enlargement  is  at  its  maximum  at  the  sixth 
cervical  vertebra  where  its  transverse  dimension  is  14  mm.  and  its 
dorsoventral  measurement  is  12  mm.  The  lumbar  enlargement  is 
greatest  at  the  twelfth  thoracic  vertebra  where  it  measures  13  mm. 
transversely  and  n  mm.  dorsoventrally.  The  outline  in  the 
cervical  region  is  oval,  in  the  thoracic  region  almost  circular,  and  in 
the  lumbar  portion  oval. 

The  increase  in  size  at  the  enlargements  is  due  to  the  added  cells 
and  fibers  for  the  appendages.  These  enlargements  vary  in  size 
according  to  the  use  of  the  appendages;  in  man,  ourang  and  gibbon 
the  cervical  enlargement  is  the  larger;  in  the  kangaroo  and  ostrich 
the  lumbar  enlargement  is  the  larger.  In  animals  without  appen- 
dages these  areas  are  only  slightly  marked  over  the  remainder  of 
the  spinal  cord. 

The  cord  ends  in  the  neighborhood  of  the  upper  border  of  the  second 
lumbar  vertebra,  and  its  termination  is  cone-shaped.  This  is  called 
the  conus  medullaris.  This  includes  the  three  lower  sacral  and  the 
coccygeal  segments.  Its  small  size  is  due  to  the  reduction  of  gray 
and  white  nerve  tissues  as  by  the  time  that  this  region  has  been 
reached  most  of  the  structures  of   the  body  have  been  supplied. 


THE   NERVE    SYSTEM 


439 


Posterior  roots 


Anterior  roots 


A — At  the  level  of  the 

sixth  cervical  nerve-roots 


Postero-median  sulcus 


Anterior  fissure 


B — At  the  mid-thoracic  region 


Central  canal 


C — At  the  center  of  the 
lumbar  enlargement 


D — At  the  upper  part  of 
the  conus  medullaris 


E — At  the  level  of  the 

fifth  sacral  nerve-roots 


F — At  the  level  of  the 
coccygeal  nerve-roots 

Fig.  247. — Sections   through   Different  Regions   of   the   Spinal   Cord. 

(Morris  after  Schwalbe.) 


44-0  PRACTICAL   HISTOLOGY 

Owing  to  the  fact  that  the  cord  is  shorter  than  the  vertebral  canal, 
the  lower  lumbar,  the  sacral  and  coccygeal  nerves  pass  down  for 
varying  distances  before  reaching  their  respective  foramina.  This 
produces  a  mass  of  fibers  in  the  lower  part  of  the  canal  called  the 
cauda  equina.  In  the  center  of  the  latter  is  a  fibrous  band  that 
extends  toward  the  end  of  the  canal.  It  is  the  filum  terminate. 
This  consists  chiefly  of  pia  and  is  about  25  cm.  in  length.  One-half 
lies  within  the  dural  sac  and  the  remainder  extends  beyond  it.  Its 
peripheral  end  is  attached  to  the  coccyx. 

The  cord,  upon  section,  consists  of  two  hemispheres  separated 
ventrally  by  the  ventral,  or  anterior  median  fissure,  in  which  is 
seen  a  process  of  the  pia.  Dorsally  no  fissure  exists,  but  a  septum  is 
present.  This  is  the  dorsal  or  posterior  medium  septum,  or  raphe. 
The  gray  substance  of  the  cord  is  arranged  in  the  form  of  a  letter 
H,  the  two  side  bars  constituting  the  horns,  and  the  cross-bar  the 
gray,  dorsal,  or  posterior  commissure.  The  horns  are  further 
subdivided  into  ventral,  or  anterior,  and  dorsal,  or  posterior.  In 
the  thoracic  region  a  lateral  horn  is  described. 

The  ventral  horns  are  large  and  blunt,  and  do  not  extend  to  the 
periphery.  In  them  are  found  collections  of  large,  multipolar 
ganglion  cells  having  a  motor  function.  The  axis  cylinders  of  the 
cells  pass  out  of  the  ventral  portion  of  the  cord  as  the  ventral  root 
of  the  spinal  nerve.  These  cells  average  60  to  120  microns,  and  are 
quite  numerous.  Each  is  surrounded  by  a  distinct  lymph  space. 
They  are  collected  into  various  groups  which  vary  according  to  the 
region  of  the  cord.     The  following  are  the  most  important. 

1.  The  ventromedial  group  is  found  in  nearly  all  segments  of  the 
spinal  cord  (except  in  the  fifth  lumbar  and  first  sacral  segments). 
This  apparently  represents  the  nuclei  of  origin  of  the  nerve  fibers 
that   supply    the    long    trunk    muscles. 

2.  The  dorsomedian  group  is  found  in  the  upper  cervical,  the 
thoracic  and  first  lumbar  segments,  that  is  where  no  limb  muscles 
are  represented. 

3.  4.  The  ventrolateral  and  dorsolateral  groups  are  the  largest  and 
represent  the  nuclei  or  origin  of  the  motor  nerves  of  the  muscles  of 
the  limbs.  They  are  found  in  the  cervical  and  lumbar  enlargements 
and  the  upper  sacral  segments. 


THE    NERVE    SYSTEM 


441 


5.  The  central  group  is  found  chiefly  in  the  lumbar  and  sacral 
segments. 

6.  The  intermediate,  or  lateral  group  is  a  thin  continuous  column 
of  cells  in  the  thoracic  and  first  two  lumbar  segments  with  recru- 
descences in  the  upper  cervical  and  third  and  fourth  sacral  segments. 
This  group  represents  the  splanchnic  efferent  fibers  (white  rami 
communic antes)  that  pass  from  the  cerebrospinal  system  to  the 
sympathetic  ganglia. 


Fig.  248. — Diagram  of  the  Various  Tracts  of  the  Spinal  Cord  and  Their 
Origin  or  Termination.     (Radasch,  "Manual  of  Anatomy.") 


Although  many  of  the  axones  of  the  above  cells  form  the  nerve 
fibers  of  the  ventral  roots  of  the  spinal  nerves,  the  axones  of  other 
cells  have  a  different  course  and  function.  Some  of  these  axones 
as  well  as  myelinate  dendrites,  pass  to  the  medial  and  lateral  sides 
of  the  ventral  horns  and  form  the  ventral  and  lateral  ground  bundles. 
Upon  entering  these  bundles  the  fibers  branch  T-like  and  the  di- 
visions pass  up  and  down  for  one  or  two  segments  and  then  turn 
into  the  gray  substance  to  end  around  the  cells  of  the  ventral  horns 


442  PRACTICAL   HISTOLOGY 

of  those  segments.  These  fibers  represent  intersegmental  association 
fibers  and  serve  to  connect  several  segments  together  for  coordination 
of  action  of  several  muscles,  or  muscle  groups.  Other  cells,  especially 
those  along  the  medial  side  of  the  ventral  horns,  send  their  axones 
and  dendrites  through  the  gray  commissure  to  the  other  side  of  the 
cord  as  commissural  fibers.  The  dendrites  pass  to  the  ventral  horn 
cells  of  the  same  level  and  they  do  not  leave  the  gray  substance. 
The  axones  that  cross  enter  the  ground  bundles  of  the  opposite 
side,  branch  T-like,  and  the  ascending  and  descending  branches 
ultimately  end  in  the  gray  substance  a  few  segments  above  and 
below,  terminating  around  the  cells  of  the  ventral  horn. 

The  dorsal,  or  posterior  horns  are  sharp  and  pointed,  and  usually 
extend  to  the  edge  of  the  cord.  The  cells  here  are  small  in  number 
and  size,  averaging  from  15  to  20  microns,  and  are  scattered  along 
the  external  margin.  They  comprise  marginal  cells  that  lie  near  the 
extremity  of  the  dorsal  horn  and  whose  axis  cylinders  pass  into  the 
lateral  columns  after  passing  through  the  substantia  gelatinosa; 
spindle-shaped  cells  are  the  smallest  and  neurits  of  these  pass  into 
the  dorsal  columns;  stellate  cells,  the  axis  cylinders  of  which  pass  into 
the  dorsal  columns  of  Burdach. 

Along  the  median  edge  of  the  dorsal  horn,  near  its  junction  with 
the  gray  commissure,  lies  the  only  distinct  group  of  cells  that  extends 
from  the  cervical  to  the  mid-lumbar  region.  This  is  the  nucleus 
of  Clark.  A  similar  collection,  though  less  distinct,  lies  just  ventral 
of  Clark's  column  and  extends  through  a  greater  part  of  the  cord. 
This  is*  the  nucleus  of  Stilling  and  is  represented  in  the  oblongata 
by  the  accessory  cuneate  nucleus.  Most  of  the  axones  of  these  cells 
pass  to  the  dorsolateral  columns  of  the  same  side  forming  the  posterior 
spinocerebellar  tract;  the  rest  pass  through  the  gray  commissure 
to  the  opposite  side,  possibly  to  the  white  substance,  constituting 
axones  of  commissural  cells. 

The  lateral  horns  are  most  marked  in  the  thoracic  and  upper 
cervical  and  third  and  fourth  sacral  regions.  Each  is  formed,  chiefly, 
by  the  intermediate  cell  group.  The  axones  of  these  cells  probably 
do  not  pass  into  the  ventral  roots  but  terminate  within  the  cord 
at  various  levels  of  the  same  and  opposite  sides.     They  are  probably 


THE    NERVE    SYSTEM 


443 


closely  connected  with  the  sympathetic  system  and  are  vasomotor 
and  sweat-gland  nerves. 


10 


13     12 


is 


Fig.  249. — Cross-section  of  Human  Spinal  Cord  at  Lower  Cervical  Region. 
From  Decapitated  Criminal.     (Dr.  H.  H.  Cushing.) 

1,  Ventral  spinal  artery;  2,  pial  process  in  ventral  fissure;  3,  dura;  4,  nerve 
fibers  from  ventral  horn  (motor  root  fibers);  5,  stellate  cells  of  ventral 
horn;  6,  ventral  horn;  7,  dorsal  horn;  8,  nerve  fibers  of  dorsal  horn  (sensor 
root  fibers);  9,  dorsal  septum;  10,  dorsal  spinal  artery  and  vein  (arteria  et 
vena  fissuras  posterioris) ;  n,  fibers  of  the  column  of  Goll;  12,  tissue  separat- 
ing the  columns  of  Goll  and  Burdach;  13,  column  of  Burdach;  14,  traces 
of  the  lateral  horn;  15,  fibers  of  the  lateral  columns;  17,  central  canal  in 
the  gray  commissure;  18,  ventral,  or  white  commissure;  19,  fibers  of  the 
ventral  columns;  20,  arteria  et  vena  fissurae  anterioris. 


In  the  dorsal  horn  is  the  substantia  gelatinosa  Rolandi,  which 
consists  of  cells  of  the  second  type  (Golgi). 


444 


PRACTICAL  HISTOLOGY 


The  gray  commissure  consists  of  myelinated  and  amyelinated 
commissural  fibers  separated  into  ventral  (smaller)  and  dorsal 
(larger)  bands  by  the  central  canal  of  the  cord.  The  ventral  portion 
is  called  the  ventral,  or  anterior  gray  commissure,  while  the  other 
receives  the  name  of  dorsal,  or  posterior  gray  commissure.  The 
whole  is  the  gray,  or  dorsal  commissure,  in  contradistinction  to 
the  ventral,  or  white  commissure. 


Fig.  250. — Cross-section*  of  Spinal  Cord  showing  Glial  Fibers  among  the 

Nerve  Fibers. 

a,  a,  Glial  fibers;  a',  same  cut  across;  »,  body  of  glial  cell;  t,  cross-section 
of  a  myelinated  nerve  fiber;  a,  axonal  of  same;  t',  small  (sensor?) 
nerve  fiber.     (Schafer  after  Ranvier.) 


The  canal  of  the  cord  is  the  remains  of  the  embryonal  cavity 
within  this  portion  of  the  nerve  system.  In  childhood,  it  is  lined 
by  simple  ciliated  elements,  the.endymal  cells.  Above,  it  com- 
municates with  the  fourth  ventricle,  and  its  form  varies  in  the 
different  portions  of  the  cord.  It  becomes  more  or  less  obliterated 
with  increasing  age,  partially  by  increased  growth  of  the  lining 
endymal  cells  and  partially  by  the  ingrowth  of  neuroglial  processes. 


THE    NERVE    SYSTEM  445 

Besides  the  nerve  cells,  processes  and  fibers,  the  gray  substance 
contains  that  peculiar  supportive  tissue  found  only  in  the  nerve 
system,  called  neuroglia.     This  substance  is  ectodermal  in  origin. 

Neuroglia  consists  of  two  varieties  of  cells,  ependymal  cells  and 
astrocytes,  which  are  spider  and  mossy.  The  spider  cells  are  com- 
posed of  thin,  flat  bodies  from  which  extend  long,  slender  processes. 
The  mossy  cells  have  short,  heavy  processes.  In  addition  to  these, 
there  are  some  cells  that  possess  large  bodies  and  few  processes. 
Fibers  that,  apparently,  have  no  connection  with  any  cell  are  seen 
passing  over  or  under  cell  bodies.  These  processes  all  interlace 
to  form  a  network  for  the  support  of  the  nerve  cells  and  their  proc- 
esses. This  substance  is  the  substantia  spongiosa.  Around  the 
central  canal  of  the  cord,  the  substantia  spongiosa  becomes  more 
modified,  and  is  called  the  substantia  gelatinosa  centralis.  The 
network  is  much  closer  in  this  region.  Around  the  dorsal  horns, 
it  forms  a  homogeneous,  striated  mass,  in  which  a  few  nerve  cells 
are  found.  This  is  the  substantia  gelatinosa  Rolandi,  caput  glio- 
sum,  or  gliosa  cornualis. 

The  white  substance  consists  of  myelinated  nerve  fibers,  con- 
nective tissue,  and  neuroglia.  Spider  cells  are  especially  numerous 
here.  The  nerve  fibers  possess  no  neurilemma,  and  are  grouped 
into  columns.  Ventrally,  they  are  separated  by  the  fissure,  and 
dorsally,  by  the  septum,  into  the  hemispheres.  Ventrally,  they 
are  connected  by  a  band  of  white  substance  that  lies  between  the 
bottom  of  the  fissure  and  the  gray  commissure.  This  is  the  white, 
or  ventral  (anterior)  commissure.  The  motor  fibers  are  usually  large, 
measuring  15  to  20  microns  in  diameter.     The  sensor  are  smaller. 

The  following  columns  are  not  found  in  any  one  section  of  the 
cord  but  represent  all  that  are  definitely  bounded.  Fig.  251  repre- 
sents merely  a  diagrammatic  section  locating  all  the  columns. 

The  ventro-medium  columns  that  lie  between  the  ventro-median 
fissure  and  the  ventral  roots  of  the  spinal  nerves;  the  lateral,  that 
lie  between  the  ventral  and  dorsal  roots,  and  are  subdivided  into 
ventro -lateral,  or  those  ventral  to  the  transverse  midline,  and  the 
dorso-lateral,  or  those  behind  the  same  line.  The  dorso-median 
columns  lie  between  the  septum  and  the  dorsal  roots  of  the  spinal 
nerves,  subdivided  into  dorsomedian  and  dorsolateral. 


446 


PRACTICAL  HISTOLOGY 


These  areas  are  further  subdivided  into  individual  columns.  In 
the  ventromedian  region,  there  are  several  groups:  (i)  the  direct 
pyramidal  tract  (fasc.  cerebro spinalis  anterior).  This  is  a  narrow 
band  of  fibers  that  lies  along  the  fissure,  and  represents  the  non- 
decussating  fibers  (10  to  15  per  cent.)  from  the  motor  regions  of  the 
brain.  The  bundle  is  separated  from  the  ventral  fissure  by  the  next 
tract.     This  tract  usually  disappears  in  the  thoracic  portion  of  the 


■&& 


Fig.  251. — Diagram  of  the  Various  Tracts  of  the  Spinal  Cord  and  Their 
Origin  or  Termination.      (Radasch,  "  Manual  of  Anatomy.") 


cord,  though  it  may  extend  into  the  lumbar  portion.  These  fibers 
decussate  in  the  white  commissure  and  end  in  the  ventral  horn 
of  the  opposite  side.     A  descending  tract. 

2.  The  sulcomarginal  tract  (fasc.  tecto spinalis)  is  found  only  in 
the  cervical  part  of  the  cord  and  consists  of  decussated  fibers  from 
opposite  quadrigemina  and  represents  a  descending  tract.  It  lies 
next  to  the  fissure,  in  the  cervical  segments  of  the  spinal  cord. 

3.  The  vestibulospinal  tract  (fasc.  vestibulospinal  is)  lies  at  ventral 


THE   NERVE    SYSTEM  447 

surface  of  the  cord  and  its  fibers  have  been  traced  into  the  sacral 
portion  of  the  cord.  It  consists  of  descending  fibers,  from  the 
vestibular  nucleus  of  the  brain  stem. 

4.  Ventral  ground  bundle  (fasc.  anterior  proprius).  This  con- 
sists of  fibers  that  arise  in  the  cord  and  end  in  the  cord,  extending 
up  and  down  for  short  distances  in  order  to  connect  the  various  seg- 
ments of  the  cord.  These  fibers  are  associative  in  function,  and  are 
ascending  and  descending. 

5.  The  ventral  spinothalamic  tract  (fasc.  spinothal  amicus  anterior) 
lies  in  the  intermediate  zone  of  the  ventral  column  and  consists  of 
axones  of  the  cells  of  the  dorsal  horn,  of  the  opposite  side,  that 
pass  through  the  white  commissure  to  form  this  tract.  These 
fibers  ascend  and  end  in  the  thalamus.  They  convey  touch  and 
pressure  impressions  from  the  opposite  side  of  the  body. 

In  the  lateral  region  of  the  cord  are  the  following  tracts : 
1.  Superfical  ventrolateral  spinocerebellar  (Gowers')  lies  in  the 
superficial  ventral  portion  of  the  lateral  area.  These  fibers  arise 
from  the  cells  of  the  opposite  side  of  the  cord  and  pass  through  the 
white  commissure  and  ventral  horn  to  form  this  tract.  These  fibers 
ascend  to  the  cerebellum  through  brachium  conjunctivum  and  con- 
stitute ascending  fibers  that  convey  muscle-sense  impressions,  chiefly 
from  opposite  sides  of  the  body.  They  are  concerned  with  reflex 
actions. 

2  Olivospinal  tract  (fasc.  olivospinalis)  lies  just  lateral  to  the  ven- 
tral root  and  is  found  only  in  cervical  and  upper  thoracic  portions  of 
the  cord  and  represents  descending  fibers.  This  tract  is  probably 
related  to  the  pyramidal  tract. 

3.  Direct  spinocerebellar  tract  (fasc.  spinocerebellar  is  posterior) 
lies  in  the  superficial  dorsolateral  area  and  consists  of  ascending 
fibers  from  the  cells  of  the  column  of  Clark.  This  tract  is  not 
found  in  the  lower  lumbar  region  of  the  cord.  Its  fibers  terminate 
in  the  cerebellum  reaching  this  organ  through  the  inferior  peduncles, 
(restiform  body) ;  they  carry  muscle-sense  impressions  and  are  con- 
cerned with  reflex  actions. 

4.  Crossed  pyramidal  tract  (fasc.  cerebro spinalis  posterior)  is  in  the 
dorsolateral  region  of  the  cord.  It  is  composed  of  fibers  that  arise 
from  the  pyramidal  cells  of  the  cerebral  cortex,  decussate  (85  to  90 


448  '   PRACTICAL   HISTOLOGY 

per  cent.)  in  the  oblongata,  and  end  in  the  ventral  horns  of  the  cord. 
In  the  cervical  region  it  is  internal  to  the  direct  cerebellar  tract  but  in 
the  thoracic  area  of  the  cord  it  comes  partially  to  the  surface,  and 
in  the  lumbar  region,  where  the  direct  cerebellar  tract  is  absent, 
the  crossed  pyramidal  tract  lies  entirely  superficial.  It  is  a  descend- 
ing tract. 

5.  Lateral  ground  bundle  (fasc.  lateralis  proprius)  lies  against  the 
gray  substance  and  consists  of  associative  fibers  of  both  descending 
and  ascending  courses. 

Lateral  mixed  tract  occupies  the  remainder  of  the  lateral  columns 
and  in  it  several  tracts  have  been  more  or  less  completely  outlined 
as  follows: 

6.  The  ventral  and  dorsal  spinothalamic  tracts  {fasciculi  spino- 
thalamics anterior  et  posterior)  consist  of  fibers  that  arise  from  the 
cells  of  the  dorsal  horns  of  the  opposite  side;  these  pass  through  the 
white  commissure  to  reach  these  tracts  and  pass  up  the  cord  to 
terminate  in  the  thalamus.  They  are  ascending  tracts.  The  ventral 
one  conveys  impressions  of  touch  and  pressure  and  the  dorsal  one 
(scattered  in  Gowers'  tract)  conveys  impressions  of  heat,  cold  and 
pain  from  the  opposite  side. 

7.  The  rubrospinal  tract  (fasc.  rubro  spinalis)  consists  of  axones 
that  descend  from  the  cells  of  the  red  nucleus  of  the  midbrain  to 
terminate  about  the  cells  of  the  ventral  horn.  It  is  a  part  of  the 
indirect  motor  pathway. 

8.  The  tectospinal  tract  (fasc.  tecto spinalis)  consists  of  descending 
axones  from  the  cells  of  the  quadrigemina.  These  terminate  about 
the  cells  of  the  ventral  horn. 

9.  The  spinotectal  tract  (fasc.  spinotectalis)  consists  of  ascending 
axones  of  the  cells  of  the  dorsal  horn  and  they  terminate  about  the 
cells  of  the  corpora  quadrigemina. 

These  last  three  tracts  collectively  are  also  termed  the  fasciculus 

intermedius. 

In  the  dorsal  region  are  seen  the  following  tracts: 

1 .  Fasciculus  gracilis  (column  of  Goll)  lies  adjacent  to  the  dorso- 

median  septum  and  consists  of  ascending  fibers  that  arise  in  the  cells 

of  the  spinal  ganglia  (the  axonic  processes).     These  fibers  end  in 

the  nucleus  gracilis. 


THE   NERVE   SYSTEM  44C) 

2.  Fasciculus  cuneatus  (column  of  Burdach)  lies  peripheral  to  the 
preceding,  and  likewise  consists  of  fibers  (ascending  axones  derived 
from  the  cells  of  the  spinal  ganglia). 

As  the  fibers  of  both  bundles  enter  the  cord  they  branch  into  a 
shorter  descending  and  long  ascending  branches.  The  longer  ones 
have  been  described.  Most  of  the  short  ones  soon  end  in  the  gray 
substance  of  the  dorsal  horns  of  the  same  side  while  the  remainder 
cross  to  the  opposite  horn  through  the  dorsal  gray  commissure. 

3.  The  comma  tract  of  Schultze  (fasc.  inter fascicularis)  occupies 
a  position  in  the  tract  of  Burdach  at  the  boundary  line  with  the 
tract  of  Goll.  Its  fibers  are  descending,  and  it  consists  of  a  group  of 
the  fibers  mentioned  in  the  preceding  paragraph. 

4.  The  oval  tract  of  Flechsig  (fasc.  cervicolumbalis)  is  situated 
along  the  dorsal  septum,  is  another  group  of  the  descending  fibers. 

5.  The  marginal  tract,  or  tract  of  Spitzka,  or  Lissauer,  is  located 
along  the  dorsal  root  or  among  its  fibers.  It  consists  of  some  of  the 
axones  of  cells  of  the  spinal  ganglia,  which  traverse  not  more  than 
three  of  four  segments  and  end  around  the  cells  in  the  gliosa  cornualis. 
It  is  sensor  in  function  and  is  probably  concerned  with  transmission 
of  pain  sense. 

6.  The  septomarginal  tract  (Bruce)  is  also  associative  in  function 
and  lies  along  the  dorsal  septum.  Its  fibers  ascend  and  descend. 
Both  of  these  tracts  are  most  distinct  in  the  lumbar  region  of  the 
cord. 

7.  The  dorsal  ground  bundle  (fasc.  posterior  proprius)  lies  next 
to  the  gray  substance  of  the  dorsal  horn  and  consists  of  short  fibers 
that  ascend  and  descend;  they  are  associative  in  function. 

The  dorsal  columns  are  the  most  complex  of  the  spinal  cord.  It 
will  simplify  them  to  consider  the  course  of  the  fibers  as  they  enter 
the  dorsal  horns. 

1.  Most  of  these  fibers  form  the  fasciculi  cuneatus  and  gracilis; 
these  fibers  divide  into  ascending  and  descending  branches.  The 
former  branches  are  of  variable  length,  some  ending  soon  in  the  gray 
of  the  dorsal  horn  and  some  ending  in  the  same  way  at  higher  levels 
Some  of  the  ascending  fibers  of  each  spinal  nerve  continue  to  the 
oblongata  and  terminate  around  the  cells  of  the  nuclei  cuneatus  and 
gracilis.     The  descending  fibers,  that  form  the  oval,  comma  and 

29 


450 


PRACTICAL  HISTOLOGY 


septomarginal  tracts,  terminate  around  the  cells  of  the  gray  sub- 
stance of  the  dorsal  horns. 

2.  Some  of  the  fibers  after  entering  the  dorsal  root  zone  course 
along  the  medial  side  of  the  gray  of  the  dorsal  horn  and  then  enter 
it  to  terminate  about  the  cells  of  the  same  level.  They  are  concerned 
in  reflex  actions. 


Fig.  252. — A  Diagram  of  the  Component  Elements  of  the  Spinal  Cord 
and  It's  Nerve-roots  in  a  Trunk-segment  Illustrating  the  Four 
Functional  Divisions  of  the  Nerve  System.     (After  Johnston.) 

ss,  Somatic  sensor;  vs,  visceral  sensor;  vm,  visceral  motor;  sm,  somatic  motor. 
The  arrow  heads  indicate  the  directions  of  the  impulses.  Note  that  visceral 
motor  impulse  passes  out  through  the  dorsal  root. 


3.  Some  fibers  of  the  dorsal  roots  enter  into  the  formation  of  the 
marginal  tract  and  terminate  around  the  cells  of  the  substantia 
gelatinosa  and  perhaps  around  other  cells  of  the  ventral  and  dorsal 
horns. 

The  fiber  tracts  consist  of  extrinsic  and  intrinsic  fibers.  The  extrinsic 
fibers  are:  (a)  those  that  arise  outside  of  the  spinal  cord  and  traverse 
it  or  end  in  it;  (b)  fibers  that  arise  in  the  cord  and  pass  out  of  it. 
Under  (a)  are  the  tracts  of  Goll  and  Burdach,  the  crossed  and  direct 
pyramidal  tracts,  the  vestibulospinal,  olivospinal,  some  of  the  mixed 


THE  NERVE   SYSTEM  45 1 

lateral  and  marginal  tracts.  The  direct  cerebellar  and  Gowers' 
tracts  and  parts  of  the  mixed  lateral  tracts  come  under  (b). 

The  intrinsic  fibers  are  those  that  arise  and  end  in  the  spinal  cord 
as  the  three  ground  bundles. 

The  gray  substance  of  the  cord  can  be  subdivided  functionally 
into  the  following  categories:  (1)  somato -motor ;  (2)  viscero -motor ; 
(3)  viscero-sensor;  (4)  somato-sensor,  as  shown  in  Fig.  252.  The 
course  of  the  various  components  of  the  nerve-roots  is  likewise  shown. 

The  spinal  nerves  consist  of  ventral,  motor,  or  efferent,  and  dorsal, 
sensor,  or  afferent  roots.  Before  these  unite  to  form  the  nerve,  a 
mass  of  gray  substance  is  seen  upon  the  dorsal  root.  This  is  the 
spinal  ganglion.  The  fibers  of  the  dorsal  root  are  derived  from  the 
cells  that  lie  in  the  ganglia,  and  where  they  enter  the  cord,  a  distinct 
depression  is  noted.  The  fibers  peripheral  to  the  ganglion  represent 
myelinated  dendrites  and  those  that  enter  the  dorsal  root  of  the 
spinal  cord  represent  the  myelinated  axones.  Upon  examining  Fig. 
252  it  will  be  seen  that  the  dorsal  root  is  not  purely  sensor,  but  also 
contains  viscero-motor  fibers.  The  ventral  root  is  made  up  of  fibers 
derived  from  the  cells  in  the  ventral  horn,  and  where  they  emerge 
only  a  slight  incurving  of  the  surface  is  seen. 

THE  BRAIN 

In  order  to  consider  the  histology  of  the  brain  a  brief  and  general 
description  of  its  morphology  will  be  first  given. 

The  brain,  or  encephalon  is  the  largest  division  of  the  central  nerve 
system  and  is  located  in  the  cranial  cavity.  It  is  an  ovoid  mass  of 
gray  and  white  nerve  tissue  in  which  the  white  tissue  predominates. 
Its  weight  is  about  1400  grams  in  the  male  and  1200  grams  in  the 
female.  At  birth  it  weighs  about  400  grams  in  the  male  and  380 
grams  in  the  female.  By  the  end  of  the  first  year  it  has  usually 
doubled  its  weight  and  by  the  end  of  the  fourth  or  fifth  years  it  is 
usually  treble  the  weight  at  birth.  It  reaches  its  maximum  weight 
about  the  eighteenth  or  twentieth  years.  The  weight  of  the  brain 
depends  upon  age,  sex,  race,  intelligence,  body  weight  and  skull 
form.  Its  dimensions  are  frontooccipitally  16  to  17  cm.,  height 
(ventral  to  dorsal  surfaces)  12.5  cm.  and  laterally  13  to  14  cm. 


452 


PRACTICAL  HISTOLOGY 


For  convenience  of  description  it  is  divided  into  three  divisions, 
cerebrum,  cerebellum,  and  brain  stem.  The  parts  will  be  described 
in  order  from  the  spinal  cord  end  to  the  cerebral  hemispheres. 

The  brain  stem  comprises  the  oblongata,  pons  and  its  tegmental 
part  and  the  mid-brain. 


Fig. 


253- 


-Diagram   of   the  Ventral  Surfaces  of  the  Mid-brain  and  the 
Hind-brain.     {Morris.) 
I,   Optic    nerve;  2,  optic    chiasma;    3,  tuber  cinereum;  4,  corpus    albicans;  5, 
optic  tract;  6,  third  nerve;   7,  external   geniculate  body;  8,  internal  gen- 
•    iculate     body;  9,  fourth     nerve;   10,  fifth     nerve.      II,  sixth     nerve;   12, 
seventh  nerve;   13,  eighth  nerve;   14,  ninth  and  tenth  nerves;  15,  twelfth 
nerve;   16,  arcuate    fibers;   17,  lateral    column;   18,  decussation    of   pyra- 
mids;  19,  infundibulum;  20,  crus  cerebri;  21,   tractus  peduncularis  trans- 
versus;  22,    posterior      perforated      space;    23,    taenia      pont  s;    24,    pons 
varolii;    25,    fifth      nerve;    26,    flocculus;    27,    biventral     lobe;  28,  cornu- 
copia; 29,   olivary  body. 

The  oblongata  (myeJcnccphalon)  measures  about  12.5  cm.  in  length 
but  the  width  varies;  at  the  spinal  cord  extremity  it  is  about  10  mm. 
in  width  and  thickness  while  at  the  pontile  end  it  measures  about  17 
to  18  mm.  transversely  and  15  mm.  dorsoventrally.     It  represents  a 


THE    NERVE    SYSTEM 


453 


truncated  cone  that  is  flattened  dorsoventrally.  It  is  nearly  vertical 
indirection  and  represents  the  connecting  link  between  the  spinal 
cord  and  the  higher  centers. 

Upon  its  ventral  surface  is  the  ventromedial*  groove  that  is  inter- 
rupted in  part  by  the  motor  fibers  that  cross  from  one  side  to  the 
other  and  form  the  pyramidal  decussation.  At  each  side  of  the  groove 
is  a  tapering  cylindrical  mass  called  the  pyramid;  90  per  cent,  of  its 
fibers  cross,  as  above  mentioned,  and  the  other  10  per  cent,  continue 


Lateralgeniculate  body 


Cerebral  peduncle 


Pons 


Olive 


Pulvinar  of  thalamus 


Epiphysis 

Medial  geniculate  body 

Quadrigeminal  bodies 


Lateral  lemniscus 


Superior  cerebellar  peduncle 
—  Middle  cerebellar  peduncle 

Inferior  cerebellar  peduncle 


Fig.    254. — Diagram  of    Lateral  View  of   Mesencephalon  and  Adjacent 
Structures.     (Morris  after  Gegenbauer,  modified.) 

upon  the  same  side  for  a  variable. distance  into  the  spinal  cord  and 
then  cross.  The  lateral  area  contains,  near  the  pontile  extremity,  a 
small  ovoid  body  about  12  mm.  long  called  the  olive.  The  remainder 
constitutes  the  lateral  column  which  represents  the  continuation  of 
some  of  the  lateral  tracts  of  the  spinal  cord  (the  dorsolateral  cerebel- 
lar, Gowers'  and  lateral  ground  bundle).  The  caudal  end  of  the 
olive  is  crossed  by  the  external  (superficial)  arcuate  fibers.  In  the 
lateral  area  are  seen  the  nerve  roots  of  some  of  the  cerebral  nerves 
(hypoglossal,  spinal  accessory,  vagal  and  glossopharyngeal).  The 


454 


PEACTICAL   HISTOLOGY 


dorsal  area  in  its  caudal  portion,  shows  the  dorsornedian  groove  which 
terminates  above  at  the  lower  angle  of  the  fourth  ventricle.  The 
latter  is  bounded  upon  each  side  by  a  club-shaped  elevation,  the 
nucleus  gracilis  lateral  to  which  is  the  nucleus  cuneatus.  These 
two  nuclei,  on  each  side,  are  separated  by  a  shallow  groove,  the 
intermediate  sulcus.  At  the  upper  extremity  of  the  nucleus  is  the 
tuberculum  rolandi,  an  eminence  that  lies  in  -the  dorsolateral  sulcus 
and  causes  that  to  fork  at  this  point.  The  upper  and  median  por- 
tion of  the  dorsal  part  of  the  oblongata  is  represented  by  the  lower 
triangular  portion  of  the  fourth  ventricle  which  is  bounded  upon 
each  side  by  the  restiform  bodies  that  constitute  the  remainder  of 
the  dorsal  area.  These  bodies  consist  of  the  fibers  of  the  dorsolateral 
cerebellar  tract  (that  enter  them  from  the  lateral  columns  of  the 
oblongata  and  the  superficial  and  deep  arcuate  fibers. 

THE  PONS  AND  TEGMENTAL  PORTION  OF  THE  PONS 

The  pons  represents  the  broad  band  of  fibers  seen  upon  the  ventral 
part  of  the  middle  portion  of  the  brain  stem.  It  measures  about 
2.5  cm.  from  above  downward  and  the  lateral  boundaries  are  indi- 
cated by  the  roots  of  the  two  trigeminal  nerves.  From  these  roots 
on  the  transverse  fibers  of  the  pons  constitute  the  brachia  pontis. 
These  brachia  constitute  the  lateral  areas  of  the  pons  and  the  fibers 
continue  into  each  cerebellar  hemisphere.  In  the  pons  area  are 
seen  the  auditory,  facial,  abducent  and  trigeminal  nerves. 

The  tegemental  part  of  the  pons  cannot  be  seen  ventrally.  It 
really  represents  a  continuation  of  the  oblongata  and  has  been  well 
called  the  preoblongata.  If  a  knife  be  passed  frontally  just  dorsal 
to  the  pons  mass  and  this  be  lifted  off  then  the  tegmental  portion 
approximately,  wilhbe  exposed.  The  dorsal  surface  of  this  part  is 
the  upper  half,  or  triangle,  of  the  fourth  ventricle.  This  triangle 
is  bounded  laterally  by  the  two  overhanging,  flattened  masses  of 
fibers  that  converge  and  form  the  apex  of  the  triangle.  These  are 
the  brachia  conjunctiva.  The  so-called  floor  of  the  fourth  ventricle 
is  a  layer  of  gray  nerve  tissue  in  which  are  some  of  the  nuclei  of 
origin  and  termination  of  cerebral  nerves.  The  real  roof,  or  dorsal 
wall  is  represented  by  two  thin  membranes  called  the  superior  and 


THE   NERVE    SYSTEM 


455 


inferior  medullary  veli,  which  consist  of  a  layer  of  ependymal  cells 
reinforced  by  the  pia  and  arachnoid.  In  the  inferior  velum  there  is 
an  opening  called  the  foramen  of  Majendie  and  at  the  lateral  angles  of 
the  fourth  ventricle  are  small  openings  in  the  roof  called  the  for- 
amina of  Luschka;  at  the  sides  of  the  ventricle  are  the  lateral  recesses 
that  communicate  with  the  subarachnoid  space  of  the  ventral  sur- 
face. By  means  of  these  openings  the  cerebrospinal  fluid  within 
the  ventricular  system  can  pass  out  of  the  brain  into  the  subarach- 
noid space  and  vice  versa. 


Inferior 
quadrigeminal  body 

Trochlear  nerve 


Anterior  medullary 

velum 

Brachium 

conjunctivum 


Brachium  of  pons 


Restiform  body 

Ligula  taenia 
Chorioid  tela  of 
fourth  ventricle 

Cuneate  tubercle 
Clava 
Tubercle  of  Rolando 


Frenulum  veli 
Lateral  lemniscus 

Lingula  of  vernis 


Fourth  ventricle 


Posterior 
medullary  velum 
Chorioid  plexus 

Foramen  of  Magendie 


Obex 


Fig.  255. — Diagram  of  the  Roof  and  Lateral  Boundaries  of  the  Fourth 
Ventricle.  The  Trochlear  Nerve  should  be  shown  Emerging  from 
the  Lateral  Boundary  of  the  Frenulum  Veli.     {Morris'  Anatomy.) J 


THE  MID-BRAIN 

The  mid-brain  {mesencephalon)  is  about  18  mm.  in  length  and 
represents  the  upper  portion  of  the  brain  stem.  Upon  its  ventral 
surface  are  seen  two  very  large,  whitish  masses,  of  a  cylindrical  form, 
that  diverge  from  each  other.  These  are  the  crura  cerebri  (pedun- 
culi  cerebri) .     Each  crus  looks  like  a  rope-like  mass  of  white  fibers 


456 


PRACTICAL  HISTOLOGY 


that  starts  at  the  upper  border  of  the  pons,  but  at  a  more  dorsal 
level,  and  then  passes  upward  (frontally)  and  laterally  into  the 
cerebrum.  Between  these  diverging  crura  is  a  triangular  area 
called  the  interpeduncular  space.     From  this  the  oculomotor  nerves 


Fig.  256. — Median  Section  Through  Cerebellum  and  Brain-stem.     (Allen 

Thompson,  after  Reichert.) 

1,  Culmen  monticuli;  2,  supeiior  semilunar  lobe;  3,  inferior  semilunar  lobe;  4, 
slender  lobe;  5,  biventral  lobe;  6,  tonsil;  7,  massa  intermedia;  8,  thalamus; 
9,  epiphysis  (pineal  body);  10,  corpora  quadrigemina;  11,  declive;  12, 
cerebral  peduncle;  13,  corpus  medullare;  14,  folium  of  vermis;  15.  tuber  of 
vermis;  16,  uvula  of  vermis;  17,  pyramid  of  vermis;  18,  stria  medullaris 
thalami;  19,  third  ventricle;  20,  column  of  fornix;  21,  anterior  commissure; 
22,  lamina  terminalis;  23,  tuber  cinereum;  '24,  recessus  infundibuli;  25, 
hypophysis  (pituitary  body);  26,  aquaeductus  cerebri  (sylvii);  27,  pons;  28, 
fourth  ventricle;  29,  tela  chorioidea  of  fourth  ventricle;  30,  medulla 
oblongata. 


emerge.  At  each  lateral  area  of  the  mid-brain  are  seen  a  part  of  the 
crus,  the  medial  geniculate  body  and  the  superior  and  inferior  brachia. 
The  dorsal  surface  of  the  mid-brain  exhibits  the  corpora  quadrigemina, 


THE   NERVE    SYSTEM  457 

or  colliculi.  These  are  four  in  number,  two  superior  and  two  inferior. 
These  are  separated  from  one  another  by  a  longitudinal  and  a  trans- 
verse furrow.  The  superior  bodies  are  connected  with  eye  muscle 
reflexes  and  the  inferior  are  way-stations  in  the  auditory  pathway. 

THE  CEREBELLUM 

The  cerebellum  lies  in  the  posterior  fossa  of  the  skull  and  in  man  is 
completely  covered  by  the  occipital  pole  of  the  cerebrum.  It  weighs 
about  165  grams  in  the  male  and  155  grams  in  the  female.  It 
reaches  its  maximum  weight  between  the  twenty-fifth  and  thirty- 
fifth  years.     It  represents  an  important  coordinating  center. 

■This  structure  consists  of  two  lateral  lobes,  or  hemispheres,  and  a 
middle  lobe  or  the  vermis.  The  lobes  contain  many  fissures  that  have 
a  transverse  direction.  The  cerebellum  is  connected  with  the  rest 
of  the  nerve  system  by  three  pairs  of  peduncles  inferior,  middle  and 
superior.  The  inferior  ones  are  the  restiform  bodies  and  serve  to 
connect  the  cerebellum  with  the  spinal  cord,  oblongata  and  cerebral 
nerve  nuclei.  The  middle  ones,  the  brachia  pontis,  are  the  largest  and 
consist  of  fibers  that  mainly  connect  one  cerebellar  hemisphere  with 
the  other  through  the  nuclei  pontis.  The  superior  peduncles  are 
the  brachia  conjunctiva  and  serve  to  connect  the  cerebellar  cortex 
with  the  mid-brain  especially. 

THE  CEREBRUM 

The  cerebrum  is  the  largest  portion  of  the  brain  mass.  It  com- 
prises the  cerebral  hemispheres,  the  corpora  striata,  the  olfactory 
tracts  and  bulbs  and  these  parts  constitute  the  telencephalon.  The 
thalami,  optic  chiasm,  hypophysis,  optic  tracts  and  lateral  geniculate 
bodies  represent  the  diencephalon. 

Ventrally  are  seen  the  corpora  albicantia,  or  mammillary  bodies, 
that  are  two,  small  whitish  bodies  one  on  each  side  of  the  inter- 
peduncular space.  They  are  way-stations  in  the  olfactory  path- 
way. The  tuber  cinereum  is  a  hollow  conical  structure  just  in  front 
of  the  preceding  structures.  To  this  the  hypophysis  is  attached 
by  a  delicate  stalk.  This  is  a  glandular  structure  that  lies  in  the 
sella  turcica  of  the  sphenoid  bone.     The  optic  chiasm  represents  the 


458  PRACTICAL  HISTOLOGY 

convergence  and  decussation  of  the  fibers  of  the  optic  nerves.  These 
continue  occipitally  as  two  flattened  bands  called  the  optic  tracts. 
The  lateral  geniculate  bodies  are  small  structures  that  represent  way- 
stations  in  the  optic  pathway.  Laterally  and  dor  sally  only  the  large 
cerebral  hemispheres  are  to  be  seen.  These  constitute  about  six- 
sevenths  of  the  brain  and  they  are  separated  from  each  other  in  the 
midline  by  the  median  longitudinal  fissure.  Many  fissures  and  sulci 
are  seen  upon  the  lateral  and  medial  surfaces  of  each  hemicerebrum. 
These  tend  to  divide  the  surface  into  lobes  and  their  subdivisions. 
The  entire  surface  is  made  up  of  small  folds  called  convolutions. 
At  the  bottom  of  the  median  longitudinal  fissure  is  seen  a  broad  band 
of  white  fibers  that  connects  the  two  hemicerebri  together.  This  is 
the  call os urn  and  it  represents  a  commissure. 

THE  INTERNAL  ANATOMY  OF  THE  BRAIN  '- 

As  was  noted  in  connection  with  the  histology  of  the  spinal  cord 
the  gray  nerve  tissue  was  arranged  in  the  form  of  an  H-shaped, 
fluted  column  with  the  white  nerve  tissue  completely  surrounding 
it.  At  the  lower  part  of  the  oblongata  this  relation  is  somewhat  the 
same  with  alternations  due  to  the  motor  and  sensor  decussations. 
The  canal  of  the  spinal  cord  continues  into  the  lower  portion  of  the 
oblongata  gradually  approaching  the  dorsal  surface  until  it  is 
finally  exposed;  it  .then  spreads  and  constitutes  the  shallow  fourth 
ventricle.  This  is  formed  by  the  failure  of  nerve  elements  to  develop 
in  the  dorsal  wall  of  the  neural  tube  in  this  region  and  as  all  of  these 
elements  and  fibers  are  developed  laterally  and  especially  ventrally 
the  ventricle  is  superficially  placed.  In  the  lower  part  of  the 
oblongata  the  gray  nerve  tissue  continues  in  close  relation  with  the 
canal  and  as  this  canal  becomes  exposed  the  gray  nerve  tissue  is 
found  forming  the  so-called  floor  of  the  ventricle  and  constitutes 
the  ventricular  gray  substance.  It  is  as  though  the  cord  had  been 
split  open  along  the  dorsomedian  septum  and  the  two  halves  spread 
apart  and  the  canal  exposed  as  a  diamond  shaped  fossa   (fourth 

1  The  internal  anatomy  of  the  brain  stem  and  the  description  of  the  various 
pathways  are  taken  from  Radasch's  "  Manual  of  Anatomy"  published  by  W.  B. 
Saunders,  Phila. 


THE   NERVE    SYSTEM  459 

ventricle).  As  a  result  of  this  change  the  motor  cells  are  still 
ventrally  placed  but  mainly  near  the  midline;  the  originally  dorsal 
sensor  cells  have  been  moved  to  the  lateral  region  of  the  floor  of 
the  ventricle. 

As  the  fourth  ventricle  passes  fron tally  into  the  aqueduct  it  is  as 
though  the  slit  cord  had  again  been  restored  to  its  original  condi- 
tion and  the  gray  nerve  tissue  again  surrounds  the  entire  canal; 
the  ventral  or  floor  gray  represents  the  seat  of  cerebral  nerve  nuclei 
(chiefly  motor),  while  the  dorsal  gray  is  sensor  (connected  with  the 
optic  and  auditory  nerves).  It  is  to  be  remembered  that  all  of  the 
nerve  cells  ventral  to  a  line  drawn  transversely  through  the  spinal 
canal  are  motor  and  those  cells  that  are  dorsal  to  this  line  are  sensor. 

The  motor  cells  of  the  brain  stem  do  not  form  continuous  columns 
as  in  the  spinal  cord  but  are  grouped  into  three  interrupted  columns 
constituting  the  nuclei  of  origin  of  the  cerebral  nerves.  The  median 
{somatic)  column  represents  the  nuclei  of  origin  of  the  hypoglossal 
and  abducent  nerves.  The  next  column,  somewhat  lateral  to  the 
» preceding,  is  the  lateral  somatic  column  and  consists  of  the  accessory, 
part  of  the  vagal  and  the  facial  and  trigeminal  nuclei.  The  nerve 
fibers  go  to  the  voluntary  muscles  of  the  tongue,  larynx  and  pharynx. 
The  third,  or  splanchnic  {visceromotor)  column  is  located  farthest 
from  the  midline  of  the  motor  columns.  This  consists  of  the  glosso- 
pharyngeal, facial  and  part  of  the  vagal  nuclei.  The  cells  of  these 
last  nuclei  are  concerned  with  the  movements  of  the  smooth  muscles 
of  the  viscera  and  their  axones  pass  to  sympathetic  ganglia.  These 
cells  represent  the  intermedio-lateral  group  of  the  spinal  cord. 

The  sensor  cells  likewise  form  groups  of  cells  and  not  a  continuous 
column.  These  groups  are  more  isolated  and  lie  farthest  from  the 
mid-line.  They  represent  the  nuclei  of  termination  of  the  nerve 
of  ordinary  and  special  sense.  The  olivary,  arcuate  and  pontile 
nuclei  represent  connecting  links  between  the  cerebellum  and  the 
remainder  of  the  nerve  system. 

THE  OBLONGATA 

The  histology  of  the  oblongata  will  be  considered  in  three  cross- 
sections  in  ascending  levels,  as  at  the  motor  and  sensor  decussations 
and  the  midolivary  region. 


460 


PRACTICAL  HISTOLOGY 


Motor  Decussation. — In  the  pontile  extremity  of  the  oblongata 
the  motor  fibers  all  lie  in  a  compact  bundle  in  the  ventral  portion; 
here  they  form  the  pyramid.  In  the  spinal  cord  end,  however,  about 
90  per  cent,  of  the  fibers  cross  from  one  side  to  the  other  in  bundles 
that  interrupt  the  ventromedian  fissure.  These  represent  the  motor 
decussatioi  .  Sections  of  this  level  will  show  these  fibers  sweeping 
dorsolaterally  from  one  side  of  the  fissure  through  the  substance  of 
the  oblongata  to  the  dorsolateral  regions  where  they  form  the  crossed 


Oorfo-mejUctn  septum . 

Fasciculus  gracilis- 

NucleuS  graci  h  s  ■ 
/       Fasc.cunealus. 
/        /  Nucleus  cuneafus 


Spinal  njclevsirtruct 
flfie  triqeminaJ  nerve. 


iaf.  cerebrospinal 
fasciculus. 


Dorsal  SDinocerebe.'Izi 
fasc/ct/lus. 


Ventral  Sp/n<rcerebfltar 
fasciculus- 


70 -  'p'naf  fa£c  'cu ,rus ■ 


Fig.  257. — Section  of  the  Oblongata  at  the  Level  of  the  Motor  Decus- 
ation  (Weigert's  Stain).     The  Right  shows  the  Various  Fascic- 
uli and  Nuclei  in  Outline.      (Radasch,  "Manual  of  Anatomy.") 


pyramidal  tract  of  the  spinal  cord.  The  remaining  fibers  continue 
down  upon  the  same  side  as  the  direct  pyramidal  tract  of  the  cervical 
and  upper  thoracic  levels  of  the  spinal  cord.  Ultimately  they  cross 
to  the  opposite  side  so  that  all  of  the  fibers  terminate  upon  the 
opposite  side  from  which  they  originate  in  the  cerebrum.  The  motor 
area  of  gray,  represented  by  the  ventral  horn  of  the  spinal  cord,  is 
thus  cut  into  two  portions:  (a)  the  isolated  ventral  mass  which  is 
gradually  pushed  more  laterally  and  is  diminished  in  size  at  higher 


THE   NERVE    SYSTEM  46 1 

levels;  (b)  the  basal  part  along  the  canal,  that  represents  the  motor 
gray  of  the  floor  of  the  fourth  ventricle  in  higher  levels. 

Dorsally  a  change  is  also  noticeable  upon  the  peripheral  part  of 
the  dorsal  horn;  here  the  substantia  gelatinosa  has  become  greatly 
increased  and  forms  a  projecting  mass  upon  the  lateral  surface  of  the 
oblongata  called  the  tiiberculum  cinereum.  The  remainder  of  the 
dorsal  gray  also  shows  alterations.  Near  the  dorsal  median  septum 
an  elongated  aggregation  of  cells  makes  its  appearance  among  the 
fibers  of  the  funiculus  gracilis  and  this  is  the  nucleus  gracilis.  In  this 
nucleus  the  fibers  of  this  fasciculus  terminate.  As  the  nucleus 
increases  in  size  higher  up  it  produces  the  elevation  upon  the  dorsal 
surface  called  the  clava.  A  little  lateral  to  this  nucleus,  and  upon 
the  dorsal  horn,  another  collection  appears.  This  is  the  nucleus 
cuneatus  and  as  it  increases  in  size  it  produces  the  elevation  of  the 
same  name  upon  the  dorsal  surface.  In  this  latter  nucleus  the  fibers 
of  the  fasciculus  cuneatus  terminate.  In  the  lateral  portion  of  the 
section  lie  the  lateral  columns  and  these  fiber  tracts  pass  uninter- 
ruptedly into  the  cerebellum,  quadrigemina  and  thalamus.  They 
comprise  the  several  spinocerebellar,  spinothalamic,  spinotectal, 
rubrospinal  and  vestibulospinal  and  converse  tracts. 

The  Sensor  Decussation. — This  lies  just  cephalad  of  the  motor 
decussation  but  is  not  evidenced  upon  the  surface  of  the  oblongata. 
The  ventral  area  of  the  section  shows  the  two  pyramids,  each  a 
compact  bundle  at  the  side  of  the  ventromedian  groove.  Dorsal 
to  these  are  seen  first,  a  thin  flat  band  the  beginning  lemniscus,  or 
fillet  {lemniscus  medialis)  and  dorsal  to  this  the  decussating  sensor 
fibers.  These  fibers  arise  from  the  cells  of  the  nuclei  gracilis  and 
cuneatus  and  cross  over  to  the  opposite  side  of  the  oblongata. 
Between  these  decussating  fibers  and  the  side  of  the  canal  lie  the 
wedge-shaped  remains  of  the  filaments  of  the  hypoglossal  nerve 
sweeping  ventrally  close  to  the  pyramid.  Lateral  to  these  fibers  are 
seen  the  remains  of  the  isolated  portion  of  the  ventral  horn  some- 
what smaller  than  in  the  preceding  section.  In  the  dorsal  half  of 
the  section,  the  gray  substance  has  a  peculiar  arrangement.  Near 
the  mid-line  is  the  slender  nucleus  gracilis  and  just  lateral  to  this 
the  more  massive  nucleus  cuneatus  and  then  the  tiiberculum  cinereum. 
Superficial  to  the  tuberculum  are  seen  some  nerve  fibers  and  cells 


462 


PRACTICAL  HISTOLOGY 


that  represent  the  tractus  spinalis  nerd  trigemini  and  nucleus  tr actus 
spinalis  nerve  trigemini.  At  this  level  practically  all  of  the  fibers  of 
the  fasciculi  gracilis  and  cuneatus  have  terminated. 

Between  this  and  the  next  section  the  nuclei  cuneatus  and  gracilis 
disappear,  several  new  nuclear  masses,  olivary  nuclei,  appear;  in 
addition  a  great  mass  of  nerve  fibers,  the  format io  reticularis  appears 


Decussatifia  fibers 
rj$  '"heytmniscus 

td  laTeraJ  fasuc- 


X2SC   C^:u3 


Fig.  258. — Section  of  the  Oblongata  at  the  Level  of  the  Sensor  Decus- 
sation (Weigert's  stain;.  The  Right  Half  shows  the  Various  Fas- 
ciculi and  Nuclei  in  Outline.      {Radasch,  "Manual  of  Anatomy.") 

between  the  canal  and  the  lemnisci  and  raises  the  canal  to  a  more 
dorsal  level  until  it  is  practically  exposed  and  forms  the  fourth 
ventricle. 

Midolivary  Level. — This  section  is  markedly  different.  Upon 
each  side  of  the  ventromedian  groove  lies  the  large  motor  tract  the 
pyramids;  these  are  covered  superficially  by  some  gray  nerve  tissue, 
the  arcuate  nucleus,  and  some  nerve  fibers,  the  superficial  arcuate 
fibers.  Of  these  arcuate  fibers  some  arise  from  the  nuclei  gracilis 
and  cuneatus  of  the  same  side  and  pass  to  the  cerebellum;  others 
arise  from  the  nuclei  of  the  opposite  side,  decussate  in  the  raphe, 


THE   NERVE    SYSTEM 


463 


course  ventrally  and  pass  over  the  surface  of  the  pyramid.  Many 
of  these  fibers  are  interrupted  in  the  arcuate  nuclei  and  then  pass  to 
the  cerebellum  by  way  of  the  restiform  bodies. 

Just  dorsal  to  the  pyramids  he  the  medial  lemnisci  forming  quite 
a  thick  bundle  of  longitudinally  coursing  fibers.  They  are  separated 
from  each  other  by  the  median  raphe  which  extends  dorsally  to  the 


Nucleus  of  Hypoglossal  nerve . 
Fourth  Ventricle . 
Median  longttutllnaJ  Tatcic\ 


\  Tim.  choroidea  inferior- 
Nucleus  insertus  ■ 

Nucleus  of  Vagal  nerve. 


~! 


Tracfus  jo/ifarius. 

Descending  root  of  vestibular  nerve 

Retiform  body 


Dorsal  soino  -Cerrset/aji 
fasciculus. 


ventral  spino<eret>ellaA 

fasciculus 


ley-nenTo  olivary 
fasciculus  . 


Inf.olivvry  nucleus. 


arcuaTt\nuc;eus  Hy 

Ext.  arcuate  fibers  - 


Fig.  259. — Section  of  the  Oblongata  at  the  Level  of  the  Midolivasry  Re- 
gion (Weigert's  Stain).     The  Right  Half   shows  the  Variou  Fas- 
ciculi, Nuclei  and  Nerves  in  Outline.   (Radasch,  "Manual  of  Anatomy.") 

ventricular  gray  substance.  The  raphe  consists  of  a  few  nerve  cells 
and  fibers.  Some  of  these  fibers  run  longitudinally,  others  obliquely 
(the  internal  arcuate  fibers)  and  still  others  course  dorsoventrally 
(the  external,  or  superficial  arcuate  fibers). 

Dorsally  between  each  lemnuscus  and    the  floor  of  the  fourth 
ventricle,  on  each  side  of  the  raphe,  is  seen  the  formatio  reticularis. 


464  PRACTICAL  HISTOLOGY 

This  consists  of  bundles  of  nerve  fibers  that  run  longitudinally  and 
transversely  and  some  gray  nerve  tissue.  The  hypoglossal  nerve 
divides  this  field  into  two  parts.  That  which  lies  medial  to  the 
nerve  is  called  the  formatio  reticularis  alba,  as  it  contains  very  few 
nerve  cells;  that  lateral  to  the  nerve  is  the  formatio  reticularis  grisea, 
as  it  contains  many  nerve  cells.  The  transverse  fibers  are  chiefly 
internal  (deep)  arcuate  and  olivocerebellar  while  the  longitudinal 
fibers  are  chiefly  associative  (short  course)  of  the  centers  of  respira- 
tion (nuclei  of  the  facial,  phrenic  and  vagal  nerves)  derived  from  the 
cells  of  the  grisea.  One  especial  group  of  longitudinal  fibers  just 
beneath  the  ventricular  gray  is  called  the  median  longitudinal 
fasciculus.  This  consists  of  longer  association  fibers  that  correspond 
to  the  ventral  ground  bundles  of  the  spinal  cord.  They  connect 
the  various  cerebral  nerve  nuclei  together.  The  fibers  just  ventral 
to  this  bundle  constitute  the  tectospinal  tract. 

Just  dorsal  to  and  a  little  to  the  side  of  the  pyramid  lies  a  crinkled 
mass  of  gray  nerve  tissue  containing  white  fibers  and  surrounded 
by  white  fibers.  This  is  the  inferior  olivary  nucleus  that  produces 
the  elevation  upon  the  lateral  surface  of  the  oblongata  called  the 
olive.  Its  opening,  called  the  hilus,  is  directed  toward  the  raphe 
and  of  the  fibers  that  leave  and  enter  some  pass  to  the  olive  of  the 
opposite  side  while  others  pass  to  the  cerebellum  of  the  opposite 
side  through  the  restiform  body.  Fibers  of  the  converse  course 
are  also  present.  From  the  olive  fibers  also  pass  to  the  spinal  cord 
and  thalamus  and  vice  versa.  The  dorsal  and  medial  olivary  nuclei 
are  detached  portions  of  the  olive  proper. 

In  the  dorsal  portion  of  this  section  is  seen  the  fourth  ventricle. 
The  roof  is  thin  and  devoid  of  nerve  tissue  and  constitutes  the  tela 
choroidea  inferior.  The  floor  consists  of  a  layer  of  gray  nerve  tissue 
showing  several  aggregations  of  nerve  cells,  the  nuclei  of  some  of  the 
cerebral  nerves.  On  each  side  of  the  mid-line  is  the  nucleus  of  the 
hypoglossal  nerve.  Just  lateral  to  this  lies  a  small  group  of  cells, 
the  nucleus  intercalatus  the  function  of  which  is  not  known.  Lateral 
to  this  is  one  of  the  nuclei  of  the  vagal  nerve.  That  part  of  this  nucleus 
nearest  to  the  mid-line  is  motor  (to  the  heart)  and  the  lateral  portion 
is  sensor.  In  the  lateral  dorsal  mass  is  seen  a  large  group  of  fibers, 
the  descending  root  of  the  auditory  nerve;  just  beneath  this  are  the 


THE   NERVE   SYSTEM 


46S 


nucleus  and  fasciculus  soli  tan' us.  At  the  extreme  dorsolateral 
portion  is  the  resHform  body.  This  structure  contains  the  fibers  of 
the  direct  spinocerebellar,  cerebellospinal  tracts  of  the  spinal  cord 
and  the  internal  (deep)  and  external  (superficial)  arcuate  fibers  of 
the  oblongata  region.  Beneath  these  structures  is  seen  another 
nucleus  of  the  vagus  (the  nucleus  ambiguus)  and  fibers  of  the  vagus. 
This  nucleus  probably  represents  the  remains  of  the  isolated  portion 
of  the  ventral  horn  of  lower  levels.  Near  the  side  are  seen  the  nucleus 
and  fibers  of  the  spinal  root  of  the  trigeminal  nerve. 

THE  PONS  AND  PARS  DORSALIS  PONTIS 

This  portion  practically  represents  a  continuation  of  the  oblongata 
with  the  pons  added  ventrally.  Three  sections,  lower,  middle  and 
upper  will  be  considered. 


Nucleus  globosus         Nucleus  tecti 


Nucleus  emboliformis 


Nucleus  dentatus- 


Bechterew's  nucleus 

Deiter's  nucleus 

Spinal  root  of  V  Nerve 


Brachium 
conjunctivum 

Corpus 
restiforme 

jjH  Nucleus  VI  Nerve 
Brachium  pontis 


VIII  Nerve 


Nucleus  of  VII  Nerve     Superior    Thalamoliv- 
olive  ary  tract 


Pons        Pyramid     Medial  lemniscus 


Fig.  260. — Section  of  the  Lower  Part  of  the  Pons  Region. 
(Radasch,  "Manual  of  Anatomy.") 

Lower  Section. — The  ventral  portion  of  this  section  consists 
of  a  thick  band  of  transversely  coursing  fibers  (pars  basalis  pontis) 
and  two  large  bundles  of  longitudinal  fibers,  the  pyramids.  The 
transverse  fibers  are  more  abundant  in  man  than  in  any  other 
animal  and  between  the  fibers  are  seen  collections  of  nerve  cells 

30 


466  PRACTICAL  HISTOLOGY 

that  are  the  nuclei  pontis.  Most  of  the  fibers  are  ventral  to  the 
pyramids  and  they  serve  to  connect  the  cerebellar  hemispheres 
with  each  other.  At  the  lateral  boundaries  of  the  pons  these  fibers 
collect  into  a  compact  bundle  and  enter  the  corresponding  cerebellar 
hemisphere  as  the  brachium  pontis.  Some  of  the  pons  fibers  ter- 
minate around  the  cells  of  the  nuclei  pontis  of  the  same  side  and 
others  pass  to  the  nuclei  of  the  opposite  side;  new  fibers  then  arise 
and  go  to  the  cerebellar  hemispheres.  Some  of  the  cells  of  the  nuclei 
pontis  are  also  way-stations  in  the  pathway  of  the  cerebropontile 
fibers  and  new  fibers  arising  here  pass  to  the  cerebellar  hemispheres. 
The  cerebropontile  fibers  have  a  longitudinal  course. 

In  the  area  just  dorsal  to  the  pons  fibers  are  the  pyramids.  Some 
of  these  longitudinal  fibers  terminate  in  the  nuclei  pontis  and  are  the 
cerebropontile  fibers.  Dorsal  to  the  pyramids  are  seen  a  variable 
number  of  deeper  transverse  pontile  fibers.  The  arcuate  nuclei  and 
fibers  of  the  oblongata  are  analogous  to  the  pontile  nuclei  and  fibers. 

Dorsal  to  the  pons  lie  the  fibers  of  the  medial  lemniscus  forming  a 
rather  compact  bundle  upon  each  side  of  the  raphe.  In  higher  levels 
these  lemnisci  diverge  from  the  mid-line  to  make  way  for  the 
trapezium. 

The  Pars  Dorsalis  Pontis. — The  lemnisci  separate  the  pons  proper 
from  the  pars  dorsalis  (preoblongata).  Dorsal  to  the  outer  side  of 
the  lemniscus  is  seen  the  central  tegmental  tract  and  the  superior 
olivary  nucleus  connected  with  the  fibers  of  the  trapezium  (acoustic 
fibers).  Between  the  superior  olivary  nucleus  and  the  forma tio 
reticularis  lies  a  bundle  of  fibers  (trapezial)  that  form  the  trapezium 
of  the  next  level.  This  portion  also  shows  the  formatio  reticularis 
on  each  side  of  the  raphe  with  the  median  longitudinal  fasciculus 
in  the  dorsal  area;  between  the  formatio  reticularis  and  the  cavity 
of  the  ventricle  is  seen  the  ventricular  gray  substance  in  which  certain 
cerebral  nerve  nuclei  are  seen. 

Near  the  mid-line  is  seen  the  nucleus  incertus  (Streeter)  that  con- 
tinues up  to  the  aqueduct.  To  the  side  of  this  lies  the  nucleus  of 
the  abducent  nerve;  lateral  to  this  the  principal  vestibular  nucleus 
is  noted  and  beneath  the  gray  the  descending  root  of  the  vestibular 
nerve;  at  the  dorsal  margin  lies  the  upper  end  of  the  restiform  body. 
Deeper  ventral  and  over  the  superior  olivary  nucleus  is  the  nucleus 


THE    NERVE    SYSTEM 


467 


of  the  facial  nerve  while  lateral  thereto  are  some  of  the  fibers  of  this 
nerve.  Between  the  facial  nerve  and  the  restiform  body  are  found 
the  substantia  rolandi  and  the  descending  root  of  the  trigeminal  nerve. 
Trigeminal  Nerve  Level. — The  ventral  portion  of  this  section 
shows  the  superficial  and  deep  fibers  of  the  pons  embracing  Uie  two 
pyramids.  At  the  sides  the  brachia  pontis  are  present.  At  the 
junction  of  the  pons  with  the  tegmental  portion  the  medial  lemnisci 
have  been  pushed  to  the  side  and  replaced  by  the  trapezium,  a  set  of 
transverse   fibers  (decussating)  interspersed   with  nerve  cells  (the 


Fourth 
ventricle 
Dorsal  longitu- 
dinal fasciculus 
Median    longi- 
tudinal fascic- 
ulus 

Formatio  retic- 
ularis 

Trapezium  and 
medial  lemnis- 
cus 

Deep  fibers  of 
pons 


Pyramis 


Superficial 
fibers  of  pons 


Fig.   261.- 


Brachium  con- 
junctivum 

Desc.  motor 
root  of  the  tri- 
geminal nerve 

Sensor  nucleus 
of  trig,  nerve 

Motor  nucleus 
of  trig,  nerve 

Thalmoolivary 
tract 

Lateral  lemnis- 
cus 

Brachium 
pontis 


-Section  of  the  Pons  at  the  Level  of  the  Origin  of  the  Tri- 
geminal Nerve.      (Radasch,  "  Manual  of  Anatomy.") 


trapezial  nucleus).  These  fibers  arise  from  the  ventral  and  some 
from  the  dorsal  cochlear  nuclei  of  the  floor  of  the  fourth  ventricle 
and  pass  to  the  trapezium  where  some  of  the  fibers  terminate  in  the 
nucleus  trapezoideus  of  the  same,  or  opposite  side  while  some  ter- 
minate in  the  olivary  nuclei  of  the  same  or  opposite  side.  The  new 
fibers  from  the  cells  then  cross  to  the  opposite  side  (if  the  preceding 
have  not)  making  the  decussation  complete;  these  fibers  are  then 
joined  by  new  fibers  from  the  cell  of  the  opposite  side  and  form  the 
lateral  lemniscus.     The  trapezium  and  lateral  lemniscus  are  parts 


468  PRACTICAL  HISTOLOGY 

of  the  auditory  pathway.  Between  the  trapezium  and  the  lateral 
surface  of  the  section  are  seen  the  superior  olivary  nucleus,  the  fibers 
of  the  motor  root  of  the  trigeminal  nerve,  while  more  ventral  are  the 
brachium  ponlis  and  the  sensor  root  of  the  trigeminal  nerve.  Near  the 
surface*  lies  the  sensor  root  of  the  latter  nerve. 

Dorsal  to  the  trapezium  and  in  the  mid-line  is  the  raphe  with  the 
formatio  reticularis  forming  a  large  field  upon  each  side.  Lateral 
to  the  formatio  reticularis  is  the  motor  nucleus  of  the  trigeminal  nerve 
and  upon  the  surface  is  the  superior  cerebellar  peduncle  {brachium 
conjunctivum)  forming  also  the  dorsal  wall  of  this  section.  The 
peduncle  is  semilunar  in  shape,  on  section,  and  consists  chiefly  of 
fibers  from  the  cells  of  the  dentate  nucleus  of  the  cerebellum  while 
the  remainder  are  probably  from  the  cerebellar  cortex  of  the 
opposite  side,  decussating  to  reach  this  side.  These  fibers  pass 
chiefly  to  the  red  nucleus  of  the  mid-brain,  but  some  continue  to  the 
thalamus. 

In  the  dorsal  portion  of  this  section  the  fourth  ventricle  is  seen 
becoming  narrower  and  is  roofed  by  the  valvula,  or  anterior  medullary 
velum.  Beneath  the  ventricular  gray  and  near  the  mid-line  is  the 
median  longitudinal  fasciculus. 

The  Upper  Level. — A  section  through  this  part  is  smaller  and  more 
compact.  In  the  ventral  area  the  pyramids  are  separated  into  small 
bundles  by  the  transverse  pontile  fibers.  The  trigeminal  nerve  is 
seen  at  the  side  of  the  field.  The  tegmentum  shows  changes.  In 
the  midline  and  dorsal  to  the  pons  fibers  the  decussating  fibers  of 
the  brachia  conjunctiva-  replace  the  trapezium  and  the  somewhat 
flattened  medial  lemniscus  is  seen  at  the  side  of  the  section.  The 
formatio  reticularis  lies  just  dorsal  to  the  decussating  fibers  and 
laterally  is  the  deeply  placed  brachium  conjunctivum,  covered  by 
the  flattened  band-like  lateral  lemniscus.  In  the  lateral  lemniscus 
are  some  nerve  cells  that  constitute  the  nucleus  to  this  tract  and 
probably  represent  a  continuation  of  the  superior  olivary  nucleus. 
In  this  nucleus  some  of  the  fibers  (from  the  ventral  cochlear  nucleus) 
terminate  and  new  ones  arise  from  the  cells  of  the  nucleus  and  con- 
tinue in  this  tract  to  end  in  the  inferior  quadrigeminum  and  medial 
geniculate  body  and  possibly  in  the  superior  quadrigeminum.  The 
dorsal  median  area  of  the  formatio  reticularis  is  occupied  by  the 


THE   NERVE    SYSTEM  469 

median  longitudinal  fasciculus.  Dorsal  tjo  this  area  is  the  ven- 
tricular gray  substance.  In  this  section  the  fourth  ventricle  is  small 
and  entirely  roofed  over  by  the  valvula  which  contains  a  little  nerve 
tissue.  At  the  lateral  boundary  of  the  ventricular  gray  is  seen  the 
mesencephalic  root  of  the  trigeminal  nerve. 

THE  MID -BRAIN 

Two  sections,  one  through  the  inferior  and  the  other  through  the 
superior  quadrigemina,  will  be  described  here. 

Inferior  Quadrigeminal  Level  (Postgeminal). — This  shows  a 
great  change  over  the  preceding  section.  In  the  ventral  area  are 
seen  the  two  crura  cerebri  separated  by  the  interpeduncular  space. 
Each  crus  consists  of  a  ventral  area,  the  crusta  (basis  pedunculi), 
containing  only  motor  fibers  in  three  groups:  (a)  the  lateral  one- 
fifth  consists  of  fibers  from  the  cortex  of  the  temporal  lobe  to  the 
nuclei  pontis  and  they  constitute  the  temp  or  0  pontile  tract;  (b)  the 
middle  three-fifths  consists  of  the  fibers  from  the  pyramidal  cells  of 
the  motor  area  of  the  frontal  lobe  passing  to  the  cerebral  nerve 
nuclei  and  to  the  spinal  cord,  constituting  the  pyramidal  tract 
previously  mentioned;  (c)  the  medial  one-fifth  consists  of  fibers  from 
the  cells  of  the  frontal  lobe  passing  to  the  nuclei  pontis  and  these 
constitute  the  fr onto pontile  tract.  Dorsally  the  crus  is  bounded  by  a 
crescentic  mass  of  pigmented  gray  substance  called  the  substantia 
nigra.  This  separates  the  tegmentum  from  the  crusta;  the  cells 
send  their  axones  in  various  directions  bat  their  function  is  unknown. 
The  substantia  nigra  extends  throughout  the  mid-brain.  The  teg- 
mentum consists  of  transverse  and  longitudinal  fibers  with  collections 
of  nerve  cells  here  and  there.  It  represents  a  continuation  of  the 
tegmental  portion  of  the  pons.  In  the  midline  is  seen  the  raphe 
and  at  the  side,  above  the  substantia  nigra,  lies  each  brachium  con- 
junctivum  completing  its  decussation.  Lateral  to  this  is  the  medial 
lemniscus.  Dorsal  to  the  brachium,  near  the  midline,  is  seen  the 
median  longitudinal  fasciculus,  while  near  the  surface  is  located  the 
lateral  lemniscus  covered  by  the  inferior  brachium.  Dorsal  to  the 
raphe  is  the  aqueduct  gray  substance,  containing  a  small  canal,  the 
iter,  or  aqueduct  (aqueductus  cerebri).     The  gray  substance  surrounds 


47o 


PRACTICAL   HISTOLOGY 


the  canal  completely;  in  its  floor  and  resting  upon  the  median  lon- 
gitudinal fasciculus,  is  a  collection  of  nerve  cells,  the  nucleus  of  the 
trochlear  nerve.  At  the  side  of  the  gray  is  the  mesencephalic  root  of 
the  trigeminal  nerve.  Dorsal  to  the  aqueduct,  on  each  side  of  the 
midline,  is  a  rounded  mass  of  gray  nerve  tissue  covered  by  white 
fibers,  the  inferior  quadrigeminal  body  (colliculus  inferior).  The 
nucleus  of  each  body  is  separated  from  the  aqueduct  gray  by  the 
stratum  lemnisci.  This  nucleus  receives  fibers  from  the  lateral 
lemniscus.  It  represents  a  way-station  in  the  auditory  pathway 
and  its  cells  send  fibers  to  the  thalamus. 


Fig.  262. — Transverse  Section  of  the  Mid-brain  through  the  Inferior 
Quadrigeminal  Bodies.     (Radasch,  " Manual  of  Anatomy.") 


Superior  Quadrigeminal  Level  (Pregeminal). — At  this  level  the 
substantia  nigra  and  crusta  are  practically  unchanged.  Medially, 
at  the  junction  of  the  crusta  with  the  tegmentum,  is  the  oculomotor 
sulcus  from  which  the  oculomotor  nerve  emerges.  Near  the  mid- 
line of  the  tegmentum  there  is  a  large  reddish  collection  of  nerve 
cells  called  the  red  nucleus.  This  is  circular  in  outline  and  receives 
fibers  from  the  cerebral  cortex,  corpus  striatum  and  cerebellar  cortex 
(through  the  brachium  conjunctivum) :  most  of  the  fibers  of  the  latter 
structure  terminate  here.  From  its  cells  fibers  pass  to  the  thalamus 
and  cerebral  cortex  and  to  the  spinal  cord  as  the  rubrospinal  tract. 
These  latter  fibers  decussate  almost  immediately  and  pass  down  the 
opposite  tegmentum. 


THE    NERVE    SYSTEM 


471 


At  the  side  of  the  red  nucleus  lies  the  medial  lemniscus  and  it  is 
smaller  as  many  of  its  fibers  terminate  in  the  superior  quadrigeminal 
body;  the  remainder  pass  to  the  thalamus  and  are  a  part  of  the 
general  sensor  pathway.  At  the  side  of  the  lemniscus  lies  the 
inferior  brachium.  Between  the  two  red  nuclei  lies  the  fountain 
decussation:  These  decussating  fibers  are  derived  from  the  superior 
quadrigeminal  bodies  and  cells  of  the  aqueduct  gray,  cross  the 
midline  and  join  the  median  longitudinal  fasciculus  and  pass  to 
the  nuclei  for  the  nerves  of  the  eye  muscles  and  to  the  spinal  centers 
for  movements  of  the  head  and  neck. 


Fig.  263. — Transverse  Section  of  the  Mid-brain  Through  the  Superior 
Quadrigeminal  Bodies.     {Radasch,  "Manual  of  Anatomy.") 


The  median  longitudinal  fasciculus  occupies,  relatively,  the  same 
position  as  in  preceding  sections.  Its  fibers  are  associative  in  func- 
tion with  regard  to  many  cerebral  and  spinal  nerve  centers  and 
it  is  analogous  to  the  ventral  ground  bundles  of  the  spinal  cord.  It 
especially  connects  the  quadrigemina  and  the  sensor  cerebral  nerve 
nuclei  with  the  oculomotor,  trochlear,  abducent  and  facial  nerves. 
A  special  nucleus  is  located  in  the  floor  of  the  third  ventricle  at  its 
junction  with  the  aqueduct.  The  fibers  of  the  cells  from  this  nucleus 
decussate  immediately  and  cross  to  the  opposite  side  through  the 
posterior  commissure. 

In  the  dorsal  part  of  the  section  are  the  aqueduct  and  the  aqueduct 
gray  which  surrounds  this  canal.  In  the  ventral  part  of  the  gray  is 
the  nucleus  for  the  oculomotor  nerve.     Dorsal  to  the  gray  are  the 


472  PRACTICAL  HISTOLOGY 

two  superior  quadrigeminal  bodies  (colliculi  superiores).  Each  body 
consists  of  four  layers  of  alternating  white  and  gray  nerve  tissues. 
The  white  layers  represent  the  fibers  of  the  optic  tract  and  some  from 
the  occipital  cortex.  Other  fibers  enter  from  the  lateral  and  medial 
lemnisci  representing  a  part  of  the  acousticooptic  reflex  pathway. 

THE  CEREBELLUM 

The  cerebellum,  or  little  brain  has  a  characteristic  gross  appear- 
ance, when  sectioned.  Most  of  the  gray  substance  is  externally 
located  while  the  white  substance  is  internal.  The  gray  constitutes 
the  cortex  and  the  white  is  the  medulla.  As  the  main  fissures  and 
sulci  run  transversely  the  cut  edge  of  the  cerebellum  shows  a  peculiar 
arborescent  appearance;  this  is  called  the  arbor  vita  cerebelli.  In  the 
hemispheres  the  white  tissue  predominates  while  in  the  vermis  the 
gray  is  more  abundant.  There  are  four  buried  masses  of  gray 
nerve  tissue  in  the  white  and  these  are  the  nuclei  dentatus,  fastigii, 
embolis  and  globosus.  The  nucleus  dentatus  is  the  largest  and  most 
important  and  lies  in  the  medulla  of  the  lateral  hemisphere.  It  is 
a  crinkled  mass  of  gray  substance  containing  white  fibers  that  enter 
and  emerge  by  the  hilus.  This  nucleus  is  important  in  the  indirect 
motor  pathway. 

The  cortex  consists  of  three  sharply  marked  layers,  the  (i)  mole- 
cular, the  (2)  ganglionic  and  (3)  granule  layers,  from  without 
inward. 

1.  The  molecular  layer  consists  of  a  network  of  neuroglia,  in 
which  the  dendritic  branches  of  the  cells  of  the  lower  layers  are 
found.  They  are  mostly  those  of  the  ganglionic  cells  These  den- 
drites form  a  dense  meshwork  of  fibrils  the  smaller  ones  of  which  show 
gemmules  while  the  larger  branches  are  smooth.  In  this  network 
there  are  also  some  collaterals  from  the  axones  of  the  Purkinje 
cells  that  seem  to  terminate  in  little  knobs  upon  the  cell  bodies  of 
neighboring  Purkinje  cells.  There  are  also  a  few  small  and  large 
multipolar  cells  in  the  molecular  layer.  The  smaller  cells  are  more 
numerous  in  the  superficial  portion  of  the  layer  and  are  somewhat 
stellate  in  form  with  two  to  five  slender  dendrites.  These  divide 
into  telodendrites  that  form  part  of  the  meshwork  of  the  molecular 


THE   NERVE   SYSTEM 


473 


layer.  The  axones  are  short,  run  a  horizontal  course  and  they,  with 
their  collaterals,  terminate  in  the  outer  part  of  this  layer.  The 
large  stellate  cells  are  more  deeply  placed.  The  dendrites  are  short 
and  terminate  among  those  of  the  Purkinje  cells.     The  axones  are 


1 


§fe 


-C. 


a 


<z 


B 


Fig.  264. — Vertical  Section  of  the  Human  Cerebellum. 
A,   Cerebellum,  low  power.     B,  Cerebellum  highly  magnified — a,  molecular  and 
ganglionic  layers;  b,  granule  layer;  c,  medulla;  d,  pia;   e,  cell  of  Purkinje; 
/,  cell  of  molecular  layer;  g,  cells  of  the  granule  layer.     C,  Cell  of  Purkinje. 

rather  long,  run  a  horizontal  course  and  give  off  five  or  six  collaterals 
that  with  the  terminal  portion  of  the  axone  pass  to  the  second  layer 
and  each  division  forms  a  series  of  delicate  branches  around  the 
body  of  a  Purkinje  cell  in  the  form  of  a  basket,  hence  the  name 


474 


PRACTICAL   HISTOLOGY 


basket  cells.  These  are  synapses  and  the  basket  cells  are  association 
neurons.  The  axones  of  the  cells  of  the  granule  layer  all  terminate 
in  the  molecular  layer  contributing  to  the  arborization  there. 

i.  The  ganglionic  layer,  or  layer  of  Purkinje  cells  is  characteristic 
of  the  cerebellum.     The  bodies  of  these  cells  are  very  large,  measuring 


Fig.  265. — Cross-section  of  a  Fold  of  the  Cerebellum  (Semidiagrammatic)  . 

{From  Bailey  after  Cajal.) 

A,  Molecular  layer;  B,  Granule  layer;  C,  Medulla;  a,  Purkinje  cell;  b,  basket 
cells  forming  investment  synapses  of  the  Purkinje  cells  at  d;  e,  stellate 
cells;  /,  Golgi  cell;  h,  granule  cells;  *,  dendrites  of  granule  cells;  h,  mossy 
fibers;  j,  m,  glial  cells;  n,   climbing  fibers. 

30  to  70  microns  in  diameter.  The  cytoplasm  is  fibrillar  but  contains 
no  pigment  granules.  The  nucleus  is  large,  stains  fairly  well  and 
the  nucleolus  is  prominent  and  darkly  staining.  Two  main  proc- 
esses extend  from  the  body  so  these  cells  are  of  the  bipolar  type. 
The  short  heavy  dendrite  passes  toward  the  molecular  layer  and 
quickly  divides  into  two  main  divisions;  these  rapidly  divide  and 


THE   NERVE    SYSTEM  475 

rcdivide  forming  a  dense  network  of  fibrils  that  extends  straight 
upward  and  laterally  to  the  surface  of  the  molecular  layer.  This 
network  is  peculiar  in  that  it  is  tall  and  broad  but  not  thicker  than 
the  diameter  of  the  cell  body.  The  appearance  is  more  that  of  a 
line  of  hedge  than  a  tree.  The  axones  pass  at  a  right  angle  to 
the  body  and  enter  the  granule  layer,  where  they  become  myeli- 
nated, and  continue  into  the  medulla  of  which  they  form  a  con- 
siderable part.  Numerous  axonic  collaterals  are  given  off  and  these 
return  to  the  molecular  layer  where  they  terminate  around  the  bodies 
of  neighboring  Purkinje  cells.  These  cells  are  more  numerous  at 
the  tops  than  at  the  bottoms  of  the  convolutions. 

Three  kinds  of  axones  terminate  in  relation  with  the  cells  of 
Purkinje:  (i)  those  of  some  of  the  granule  cells  that  end  in  relation 
with  its  dendrites;  (2)  those  of  the  basket  cells  that  terminate  in  a 
network  around  the  cell  body;  (3)  those  of  the  climbing  fibers  the 
branches  of  which  wind  around  all  of  the  dendritic  branches  except 
the  terminal  ones. 

2.  The  granule  layer  consists  of  a  broad  zone  of  small  and  large 
granule,  stellate  cells  and  solitary  cells.  The  small  granule  cells  are 
the  smallest  nucleated  elements  in  the  body  measuring  as  low  as 
4  microns  in  diameter.  The  axones  of  the  granule  cells  are  amyeli- 
nated  and  pass  into  the  molecular  layer  where  they  branch  T-like. 
These  branches  run  parallel  to  the  surface  between  the  dendrites 
of  the  Purkinje  cells  and  are  said  to  end  in  varicosities.  The 
dendrites  are  short  and  remain  in  the  granule  layer  where  they 
terminate  in  fine  branches  around  the  eosin  bodies.  The  latter  are 
small  masses  of  protoplasm,  containing  fine  eosinophilic  granules, 
and  are  supposed  to  represent  synapses  between  the  terminal  teloneu- 
rites  of  the  mossy  fibers  that  come  from  the  medulla  and  the  teloden- 
drites  of  the  granule  cells.  The  large  number  of  small  cells  and  the 
large  number  of  darkly  staining  nuclei  give  this  layer  its  granular 
appearance  and  name. 

The  large  stellate  cells  are  few  in  number  and  are  found  mainly 
near  the  Purkinje  cells.  These  are  cells  of  the  second  type  (Golgi) ; 
the  axones  are  short,  collaterals  numerous  and  these  terminate 
around  the  granule  cells.  The  dendrites  are  numerous  and  pass  to 
the  molecular  layer. 


476 


PRACTICAL   HISTOLOGY 


The  solitary  cells  are  some  small,  spindle-shaped  cells  the  function 
of  which  is  not  known. 

The  granule  layer  is  also  thicker  at  the  tops  of  the  convolutions, 
diminishing  as  the  base  is  reached. 

In  addition  to  the  above  structures  and  the  neuroglia  there  are 
the  mossy  and  climbing  fibers  in  the  cortex  of  the  cerebellum.  These 
represent  the  afferent  fibers  from  the  brain  stem  and  spinal  cord 
and  they  terminate  in  the  cortex.     The  mossy  fibers  are  very  coarse 


Fig.  266. — Diagram  of  a  Section  of  the  Cerebellum  Lengthwise  of  the 
Transverse  Convolutions.     Golgi's  Method.     (Koelliker.) 

gr.  Cells  of  the  granular  stratum;  n,  their  neuraxons  in  the  granular  layer 
and  «',  in  the  gray  stratum;  p,  p',  Purkinje  cells.  {From  Bailey's  "His- 
tology.") 


fibers  that  branch  in  the  medulla;  these  branches  pass  to  different 
folds,  or  lamellae.  Within  the  granule  layer  the  branches  divide, 
become  amyelinated  and  terminate  in  a  number  of  short  teleneu- 
rites  that  pass  to  the  eosin  bodies  and  end  in  relation  with  the 
axonic  branches  of  the  granule  cells.  These  branches  may  present 
varicosities.  The  climbing  fibers  are  also  afferent  fibers  that  enter 
the  granule  layer;  they  become  amyelinated  and  branch  profusely 
and  near  the  body  of  the  Purkinje  cells  these  branches  wind  about 
those  of  the  dendrites  like  a  vine.     They  are  thus  in  relation  with  all 


THE   NERVE   SYSTEM  477 

but  the  terminal  telodendrites  of  the  Purkinje  cells.  These  fibers 
come  from  the  pons. 

The  medulla  consists  of  myelinated  nerve  fibers  supported  by 
neuroglia  and  some  white  fibrous  connective  tissue.  The  fibers  are 
centrifugal  and  centripetal.  The  former  represent  the  myelinated 
axones  of  the  Purkinje  cells  that  pass  from  the  cortex  to  the  various 
nuclei  of  the  cerebellum  but  not  out  of  the  cerebellum  directly. 
The  centripetal  fibers  are  those  that  come  into  the  cerebellum  from 
outside  sources  and  represent  the  fibers  from  the  spinal  cord  and 
brain  stem;  these  are  the  mossy  and  climbing  fibers  mentioned  as 
terminating  in  the  cortex. 

The  glial  tissue  is  considerable  in  quantity  in  both  cortex  and 
medulla.  The  glial  fibers  form  a  meshwork  for  the  support  of  the 
nerve  ceils  and  processes  and  the  nerve  fibers.  In  the  cortex  the 
mossy  cells  predominate  while  the  medulla  contains  only  the  spider 
type.  The  extreme  superficial  portion  of  the  molecular  layer  pos- 
sesses no  nerve  cells  and  very  few  processes  and  here  the  neuroglia 
forms  a  rather  dense  marginal  layer. 

THE  CEREBRUM 

Besides  the  cerebrum,  there  are  other  masses  of  nerve  tissue  to  be 
considered  here.  These  are  the  olfactory  lobes,  the  pituitary  and 
pineal  bodies. 

The  gray  substance,  or  cortex  of  the  cerebrum,  is  divided  into 
layers  that  are  not  sharply  limited  from  one  another.  In  some 
regions,  five  can  be  made  out,  in  others  three,  while  four  form  the 
average  number.  In  the  occipital  lobes  eight  layers  can  be  demon- 
strated. The  cortex  is  made  irregular  by  the  formation  of  fissures 
and  convolutions,  The  latter  consist  of  a  central  mass  of  white  sub- 
stance, medulla,  covered  by  the  gray  substance,  or  cortex. 

The  cortical  layers  of  the  motor  area  are,  from  without  inward: 
(i)  molecular,  (2)  outer  polymorphous,  (3)  small  pyramidal,  (4)  large 
pyramidal,  (5)  inner  polymorphous  layers. 

1.  The  molecular  layer  consists  chiefly  of  neuroglia  and  cell 
processes;  the  latter  are  chiefly  dendrites  derived  from  the  deeper 
layers.     The   neuroglia   forms    a    meshwork    within    which    these 


478  PRACTICAL  HISTOLOGY 

dendrites  form  networks  tangential  with  the  surface  so  that  this 
layer  is  sometimes  called  the  layer  of  tangential  fibers.  The  cell- 
ular elements  are  few  in  number  and  of  the  second  type  and  represent 


-  ,  -  >   •  *        *  ■  i      .    *    •*    '  - 


fYS?    .   - 


-';, 


*   » 


-   - 


• 


IP 


. 


\  ;  r         .  I  -  ■■  '  :  -k 


Fig.  267. — Vertical  Section  of  Human  Cerebral  Cortex. 
a,   Pia;  b,  molecular  layer;  c,  small  pyramidal  cells;  d,  large  pyramidal  cells; 
e,  layer  of  polymorphous  cells;  /,  layer  of  fusiform  cells;  g,   medulla;   h, 
radial   bundles   of   myelinated   fibers   in   cortex;   *,    pial   process;   k,    large 
pyramidal  cell. 

cells  of  the  next  layer  that  have  entered  the  molecular  layer.  Their 
processes  all  remain  in  the  molecular  layer.  Peripherally  the 
neuroglia  forms  a  rather  dense  layer  as  in  the  cerebellum. 


THE   NERVE    SYSTEM  479 

2.  The  outer  polymorphous  layer  consists  of  a  narrow  band  of  ir- 
regular cells  that  may  be  collected  in  small  groups.  These  cells 
are  polygonal,  stellate  and  spindle-shaped  and  of  the  second  type. 
The  axones  remain  in  the  gray  substance  and  the  dendrites  pass 
to  the  molecular  layer  where  they  form  the  tangential  fibers.  These 
cells  are  best  developed  in  the  hippochampal  gyre  (olfactory  area) 
and  are  sometimes  called  the  cells  of  Cajal. 

3.  The  layer  of  small  pyramidal  cells  is  composed  of  several 
layers  of  cells,  apical  dendrites  of  which  extend  into  the  mole- 
cular layer  while  the  other  dendrites  remain  in  this  layer.  Some  of 
the  axis  cylinders  partially  pass  to  the  molecular  layer  (second  type) 
and  others  pass  into  the  medulla  (first  type,  or  Deiter  cell).  In  the 
latter  case,  the  axis  cylinders  give  off  branches  called  collaterals.  The 
cells  themselves  are  small,  measuring  10  to  12  microns  in  diameter, 
and  triangular  in  outline.  The  dendrites  arise  from  the  angles, 
while  the  axis  cylinder  or  neurit,  has  its  origin  at  the  middle  of 
the  base. 

4.  The  layer  of  large  pyramidal  cells  constitutes  the  widest  and 
most  important  layer.  The  cells  are  usually  20  to  50  microns  in 
diameter,  though  some  may  exceed  this.  The  dendrites  pass  to  the 
molecular  layer,  while  the  neurit  becomes  myelinated  nerve  fiber. 
These  cells  are,  therefore,  cells  of  the  first  type.  Their  outline  is 
triangular,  and  the  nucleus  is  large  and  prominent.  This  layer  is 
usually  as  broad  as  all  the  others  together. 

Among  the  cells  of  this  layer  there  are  groups  of  very  large  pyra- 
midal cells  called  the  giant  cells  of  Betz;  some  of  these  may  also  be 
in  the  small  pyramidal  cell  layer.  These  are  cells  of  the  first  type 
and  their  myelinated  axones  pass  into  the  medulla  and  later  form  the 
pyramidal  tract  (fasc.  cerebro spinalis).  This  constitutes  the  pyramid 
of  the  pons  and  all  oblongatal  regions  and  the  direct  and  crossed 
pyramidal  tracts  of  the  spinal  cord.  It  is  a  part  of  the  direct  motor 
pathway  and  is  concerned  with  the  movements  of  the  voluntary 
striated  muscles  of  the  body. 

5.  The  inner  polymorphus  layer  is  fairly  broad  and  consists  of 
cells  of  various  shapes.  These  are  small  and  large  pyramidal, 
spindleshaped,  oval,  polygonal  and  granule  cells.  The  polygonal  cells 
seem  to  predominate.    The  granule  cells  are  small  and  resemble  those 


480 


PRACTICAL  HISTOLOGY 


Cell  of  Retzius. 
Short-rayed  neuroglia  cell- 
Blood  vessel. 


%»Collateral. 


Neuraxon  of  a 
polymorphous 
nerve  cell. 


Long-rayed 
neuroglia 
cell. 


Fig.  268. — Diagram   of  the  Cerebral  Cortex. 
The  cells  on  the  right  are  drawn  from  Golgi  preparations  of  an  adult  man. 

(Lewis  and  Stohr.) 


THE   NERVE    SYSTEM  48 1 

of  the  cerebellum.  The  other  cells  are  somewhat  larger  than  the 
average  cells  of  the  small  pyramidal  layer.  Most  of  the  dendrites 
of  these  cells  pass  to  the  molecular  layer  while  the  others  remain  in 
this  layer.  The  axones  are  of  two  types;  some  pass  through  the 
white  for  a  short  distance  to  the  neighboring  convolutions  and  these 
are  the  association  fibers;  others  also  become  myelinated  and  enter 
the  medulla  and  these  are  the  projection  fibers  that  pass  to  distant 
parts  of  the  nerve  system.     These  cells  are  of  the  first  type. 

The  cells  of  Martinotti  are  second  type  cells  that  are  found  in  all 
of  the  layers  but  are  most  numerous  in  the  inner  polymorphous  layer. 
These  are  small  polymorphous  elements  the  axones  of  which  pass  to 
the  molecular  layer  and  assist  in  forming  the  tangential  fibers. 

In  the  last  three  layers,  bundles  of  myelinated  nerve  fibers  having 
a  radial  course  are  seen.  They  begin  in  the  small  pyramidal  layer, 
increase  in  number  as  they  approach  the  medulla,  and  contain, 
beside  those  fibers  derived  from  the  immediate  cortical  cells,  others 
whose  origin  is  not  definite. 

In  addition  there  are  other  myelinated  nerve  fibers  that  form 
layers  practically  parallel  with  the  surface.  The  striation  of  Bail- 
larger  is  composed  of  such  fibers  that  lie  in  the  large  pyramidal  cell 
layer.  The  striation  of  Bechtereff  consists  of  myelinated  fibers 
between  molecular  and  small  pyramidal  cell  layers.  These  represent 
afferent  fibers  and  are  best  marked  in  the  temporal  and  occipital 
lobes  (olfactory  and  visual  areas). 

The  cortex  of  the  occipital  lobe  (cuneus  or  visual  area)  consists  of 
eight  layers  and  these  are:  (1)  molecular,  (2)  outer  polymorphous, 
(3)  small  pyramidal  cell,  (4)  large  pyramidal  cell,  (5)  outer  striation 
of  Baillarger,  (6)  granule  cell,  (7)  inner  striation  of  Baillarger,  (8)  inner 
polymorphous  layers. 

The  layers  of  pyramidal  cells  are  quite  thin  and  the  giant  cells  of 
Betz  are  absent.  The  granule  cells  are  numerous  in  the  outer  layers 
and  so  may  almost  prevent  a  separation  into  layers  in  that  part  of  the 
cortex.  The  striations  of  Baillarger  are  very  distinct  and  the  tangen- 
tial fibers  are  well  developed.  Some  very  large  multipolar  cells  called 
the  solitary  cells  of  Meynert  occur  within  the  last  two  layers. 
The  medulla  consists  of  myelinated  nerve  fibers  from  various 

sources;  those  that  pass  to  the  periphery  of  the  body  from  the 
31 


482  PRACTICAL  HISTOLOGY 

pyramidal  and  polymorphus  cells  (projection  fibers) ;  others  from  the 
pyramidal  cells  that  pass  from  one  hemisphere  to  the  other  (com- 
missural fibers) ;  those  that  connect  different  areas  of  the  same  side 
(pyramidal  cells),  and  whose  axis  cylinders  are  "T "-branched,  and 
pass  into  the  cortex  sooner  or  later  (association  fibers);  lastly, 
fibers  that  come  from  distant  parts  of  the  same  or  the  other  hemis- 
phere,  or   other  parts   of   the  nerve   system   (centripetal  fibers). 

The  various  pathways  will  now  be  considered. 

The  Direct  Motor  Pathway. — This  comprises  but  two  neurons. 
The  parts  concerned  are  the  two  pyramidal  tracts  and  the  motor  por- 
tions of  the  cerebral  and  spinal  nerves. 

The  pyramidal  tract  of  each  side  consists  of  afferent  fibers  that  arise 
from  the  large  and  small  pyramidal  cells  of  the  motor  area  of  the 
cerebral  cortex.  They  pass  down  through  the  corona  radiata  into 
the  internal  capsule  occupying  the  middle  portion  thereof;  they  enter 
the  crusta  of  the  crus  cerebri,  then  the  tegmentum  of  the  pons  and 
the  ventral  area  of  the  oblongata;  in  these  three  regions  some  of  its 
fibers  pass  to  the  cerebral  nerve  nuclei  of  origin.  At  the  caudal  end 
of  the  oblongata  85  to  90  per  cent,  of  the  fibers  decussate  to  the  op- 
posite side  of  the  spinal  cord  as  the  crossed  pyramidal  tract  and  then 
end  at  various  levels  around  the  cells  of  the  ventral  horn.  The 
remaining  fibers  continue  down  the  same  side  of  the  spinal  cord,  as 
the  direct  pyramidal  tract,  to  various  levels  in  the  cervical  and  upper 
thoracic  region  and  then  pass  through  the  ventral,  or  white  com- 
missure, to  end  in  the  ventral  horn  of  the  opposite  side.  Ultimately 
all  fibers  decussate  before  they  end.  This  ends  the  first  neuron.  The 
second  neuron  comprises  the  cells  of  the  ventral  horn  and  their 
processes  that  form  the  motor  root  of  the  spinal  nerves,  on  the  one 
hand,  and  in  the  case  of  the  cerebral  nerves  comprises  the  cells  of 
the  various  nuclei  of  origin  and  their  processes  that  form  the  motor 
portion  of  the  cerebral  nerves.  These  axones  pass  out  of  the  gray 
substance,  become  myelinated  and  ultimately  end  directly  in  a  vol- 
untary striated  muscle  fiber.     This  is  the  end  of  the  second  neuron. 

First  neuron,  a  pyramidal  cell  in  the  motor  cortex  of  the  cerebrum 
and  its  axone  that  forms  a  part  of  the  pyramidal  tract  and  that 
ends  in  a  cerebral  nerve  nucleus,  or  the  ventral  gray  of  the  spinal 
cord. 


THE   NERVE   SYSTEM 


483 


Second  neuron,  the  cell  in  the  nucleus  of  origin  or  in  the  ventral 
gray  of  the  spinal  cord,  and  its  axone  that  ends  in  a  voluntary 
striated  muscle  fiber. 


Fig.  269. — Diagram  of  the  Neurons  in  the  Direct  and  Indirect  Motor 
Pathways  and  the  Connections  of  the  Cerebellum  with  the  Brain 
Stem  and  the  Spinal  Cord. 

Direct. — Neuron  1,  A  to  22;  neuron  2,  B  to  C.  Indirect. — Neuron  1,  A  (cerebral 
cortex)   to   D\  2,  D  to  E;  3,  E  to  F;    4,  F  to  g;  5,  g  to  B;  6,  B  to  C. 

I        (Radasch,  "  Manual  of  Anatomy.") 

The  Indirect  Motor  Pathway. — This  is  more  complex  and  com- 
prises six  neurons.    First,  from  the  motor  area  of  the  cerebrum  (say 


484  PRACTICAL  HISTOLOGY 

right  side)  through  the  pyramidal  tract,  as  above,  to  the  nuclei 
pontis  of  the  same  side  (right) ;  second,  from  the  nuclei  pontis  through 
the  brachium  pontis  to  the  cerebellar  cortex  of  the  opposite  (left)  side; 
third,  from  the  cerebellar  cortex  to  the  dentate  nucleus  of  the  cere- 
bellum of  the  same  (left)  side;  fourth,  from  the  dentate  nucleus 
through  the  brachium  conjunctivum  to  the  red  nucleus  of  the  opposite 
(right)  side;  fifth,  from  the  red  nucleus  of  that  side  through  the 
rubrospinal  tract  to  the  cerebral  nerve  nucleus,  or  ventral  horn  of 
the  spinal  cord  of  the  opposite  (left)  side.  The  fibers  of  the  rubro- 
spinal tract  cross  to  the  opposite  side  almost  immediately  after  leav- 
ing the  red  nucleus.  Sixth,  from  the  cerebral  nerve  nucleus,  or  the 
ventral  horn  gray  to  the  voluntary  striated  muscle  fiber.  As  seen 
above  there  are  three  crossings,  or  decussations,  the  next  to  the  last 
neuron  terminating  upon  the  opposite  side  of  the  body. 

The  Direct  Sensor  Pathway. — In  the  trunk  the  impulses  arise  at 
the  periphery  and  are  conveyed  by  the  sensor  spinal  nerves  to  the 
ganglia  on  the  dorsal  roots.  From  there  they  are  conveyed  into  the 
dorsal  column  of  the  spinal  cord  to  end  in  the  nuclei  gracilis  and 
cuneatus  of  the  oblongata  of  the  same  side.  Some  collaterals  are 
sent  into  the  dorsal  horn  gray.  New  fibers  arise  in  the  nuclei  cune- 
atus and  gracilis  and  immediately  cross,  or  decussate  to  the  opposite 
side,  forming  the  sensor  decussation,  that  lies  just  above,  or  cephalad 
of  the  motor  (pyramidal)  decussation.  These  decussated  fibers  form 
the  medial  lemniscus  that  continues  through  the  oblongata,  pons 
and  mid-brain  to  end  in  the  thalamus  of  that  side.  From  the  thalamus 
new  fibers  convey  the  impulses  through  the  internal  capsule  (occipital 
limb)  to  the  somatic  sensor  area  of  the  cerebral  cortex  (postcentral 
gyre).  In  this  pathway  three  neurons  are  required,  the  first,  from 
the  surface  to  the  nuclei  gracilis,  or  cuneatus  (the  cell  body  lying  in 
the  dorsal  ganglion);  the  second,  from  these  nuclei  to  the  thalamus; 
and  the  third,  from  the  thalamus  to  the  cerebral  cortex. 

Pathway  for  Touch,  Temperature  and  Pain. — In  the  trunk  and 
extremities,  the  first  neuron  cells  lie  in  the  ganglia  of  the  dorsal  roots 
of  the  spinal  nerves.  The  peripheral  fibers  (dendrites)  bring  the 
impulses  from  the  periphery  (organ  or  skin)  and  it  is  then  conveyed 
by  the  axone  into  the  spinal  cord  through  the  dorsal  root;  the  axones 
end  in  the  gray  substance  of  the  dorsal  horn.    .The  second  neuron  cells 


THE    NERVE    SYSTEM 


485 


lie  here  and  their  axones  cross  through  the  ventral  gray  commissure 
to  the  opposite  side  and  form  the  spinothalamic  tract  in  the  spinal 


Mic.j9*u>//i's 


_liwo.CwneaJ.usS 


Fig.  270. — The  Origins,  Decussations  and  Courses  of  the  Fibers  Forming 
the  Medial  and  Lateral Lemnisci.  Direct  Sensor  Pathway.  (Radasch, 
"Manual  of  Anatomy .") 


cord  and  in  the  oblongata  they  join  the  medial  lemniscus  to  end  in 
the  thalamus.     The  third  neuron  cells  lie  in  the  thalamus  and  the 


486 


PRACTICAL   HISTOLOGY 


axones  pass  through  the  internal  capsule  (sensor  limb)  to  the  cortical 
area  of  somatic  sensibility  (postcentral  gyre).  Some  of  the  impulses 
of  touch  and  contact  sensibility  are  conveyed  through  the  dorsal 
column  of  the  spinal  cord  (same  side)  to  the  nucleus  cuneatus  and 
gracilis.  The  new  fibers  from  these  nuclei  decussate  and  join  the 
opposite  medial  lemniscus  to  end  in  the  thalamus  of  that  side;  thus 
some  of  the  sensibility  fibers  cross  in  the  spinal  cord  at  their  entrance 
and  others  do  not  cross  until  the  above  nuclei  have  been  reached. 


*&% 


Fig.  271. — Diagram  of  the  Various  Tracts  of  the  Spinal  Cord  and  Their 
Origin  or  Termination.     (Radasch,  "Manual  of  Anatomy.") 

In  the  head  most  of  the  impulses  are  conducted  to  the  nuclei  of 
the  trigeminus,  glossopharyngeal  and  vagal  nerves  of  each  side  to 
the  ganglia  of  the  sensor  divisions;  then  they  are  conducted  to  the 
nuclei  of  termination  of  these  nerves,  in  the  fourth  ventricle.  This 
course  constitutes  the  first  neuron.  The  second  neurons  connect 
these  nuclei  with  the  thalamus  by  way  of  the  medial  lemniscus. 
The  third  neurons  connect  the  thalamus  with  the  cerebral  cortex 
as  above. 


THE   NERVE    SYSTEM 


487 


The  muscle  sense  (deep  sensibility)  impulses  of  the  trunk  and 
extremities  are  conveyed  as  follows:  The  first  neuron  connects  the 
periphery  with  the  spinal  cord  where  some  of  the  fibers  continue 
on  the  same  side  through  the  dorsal  column  to  the  nuclei  cuneatus 
and  gracilis.  From  here  the  fibers  of  the  second  nenron  convey  the 
impulses  by  way  of  the  opposite  medial  lemniscus  to  the  thalamus. 
The  third  neuron  connects  the  thalamus  with  the  cortical  area. 


Fig.  272. — Diagram  of  the  Structures  Involved  in  a  Reflex  Action. 
A,   Receptive    surface;   B,   skeletal    muscle;   C,   blood-vessel    and   sympathetic 
ganglion;  E,    spinal  nerve  attached  to  spinal  cord.     Red  indicates  motor 
and  blue  sensor  impulses.      (Radasch,  "Manual  of  Anatomy.") 

Some  fibers  pass  from  the  nuclei  gracilis  and  cuneatus  to  the  cere- 
bellar cortex;  new  fibers  pass  from  here  to  the  dentate  nucleus  of 
the  cerebellum  from  which  new  fibers  pass  to  the  thalamus  through 
the  brachia  conjunctiva. 

Some  of  the  fibers,  only,  of  the  first  neuron,  have  the  above  course. 
Others,  after  entering  the  dorsal  roots  of  the  spinal  nerves,  do  not 
enter  the  dorsal  column  but  join  the  spinocerebellar  tracts  (ventral 
and   dorsal   superficial)    to   end   in   the   cerebellar   cortex   of   the 


488  PRACTICAL   HISTOLOGY 

same  side.  The  impulses  are  then  carried  to  the  dentate  nucleus 
and  from  here  through  the  branchium  conjunctivum  to  the  opposite 
thalamus;  from  the  thalamus  the  impulses  are  conveyed  to  the 
cerebral  cortex. 

Respiration.- — Although  respiration  is  apparently  controlled  by 
the  respiratory  nucleus  that  lies  in  the  formatio  reticularis  of  the 
oblongata,  it  is  maintained  by  stimuli  carried  to  this  center  by  the 
blood  vascular  system  and  reflex  impulses  from  the  sensor  portion 
of  the  vagus  through  cells  in  the  nucleus  of  termination  of  the  vagal 
nerve  and  by  impulses  from  the  higher  respiratory  centers.  The 
respiratory  nucleus  is  connected  with  the  following  motor  nuclei: 
Facial,  vagal,  accessory,  cervical  plexus,  phrenic,  brachial  plexus 
and  thoracic  nerves.  Axones  from  the  higher  centers  and  from  the 
sensor  vagal  nucleus  end  in  the  respiratory  nucleus.  The  cells  of  the 
respiratory  nucleus  send  their  axones  directly,  or  by  means  of  col- 
laterals, in  the  formatio  reticularis,  to  the  nuclei  of  the  above- 
mentioned  motor  nerves  so  that  through  this  connection  a  number 
of  cerebral  and  spinal  nerves  are  caused  to  act. 

OLFACTORY  LOBE 

The  olfactory  lobe,  that  portion  of  the  nerve  system  devoted  to 
the  sense  of  smell,  is  comparatively  small  in  man.  There  are  jive 
layers  present,  which  are  best  marked  in  the  central  part  of  the 
organ.  These  are  the  layer  of  peripheral  fibers,  the  glomerular 
layer,  the  molecular  layer,  the  layer  of  mitral  cells  and  the  granule 
layer. 

The  layer  of  peripheral  fibers  consists  of  a  plexus  formed  by  the 
fibers  of  the  olfactory  nerves.  These  fibers  are  the  axone  processes 
of  the  nerve  cells  (olfactory  cells)  of  the  olfactory  mucosa  and  are 
on  their  way  to  the  next  layer. 

The  glomerular  layer  lies  internal  the  above,  and  is  made  up  of 
peculiar  round,  or  oval,  bodies  ioo  to  300  microns  in  diameter. 
They  are  said  to  be  masses  of  interlacing  telodendria  of  the  olfactory 
and  mitral  cells.  In  addition  there  are  some  Golgi  cells  (perigang- 
lion  cells) .  This  layer  constitutes  the  end  of  neuron  I  and  the  begin- 
ning of  neuron  II  of  the  olfactory  pathway. 


THE   NERVE    SYSTEM  489 

The  molecular  layer  is  made  up  of  large  and  small  spindle-shaped 
ganglion  cells  whose  dendrites  end  in  the  glomeruli;  the  axis  cylin- 
ders of  the  small  cells  (Golgi  cells)  pass  to  the  fifth  or  granule 
layer  and  these  cells  are  associative  in  function.  The  axones  of  the 
large  (brush)  cells  pass  to  and  through  the  granule  layer  to  continue 
as  a  part  of  the  olfactory  tract  with  the  fibers  from  the  mitral  cells. 
Both  of  these  sets  of  axones  represent  neuron  II. 


Fig.   273. — Diagram  of  the  Olfactory  Bulb  and  the  Cells  of  the  Olfac- 
tory Mucosa. 

C,  Olfactory  cells;  N.F.,  layer  of  peripheral  nerve  fibers;  Gl.,  glomerular 
layer;  M,  layer  of  mitral  cells;  Gr.,  granular  layer  through  which  the 
axones  of  the  mitral  cells  pass  to  the  olfactory  tract  giving  off  collaterals  to 
the  bulb;  a,  afferent  nerve  fiber  terminating  in  the  olfactory  bulb.  {After 
S  chafer.) 

The  layer  of  mitral  cells  consist  mainly  of  large  pyramidal  cells 
varying  in  size  from  30  to  50  microns.  Their  dendrites  pass  to  the 
glomeruli  and  the  axis  cylinders  through  the  granule  layer  to  the 
olfactory  tract  to  end  ultimately  in  the  brain.     Also  neuron  II. 

The  granule  layer  consists  of  nerve  cells  and  fibers.  The  cells  are 
stellate,  ganglion  elements,  and  peculiar  granule  cells;  the  latter 
appear  to  have  no  axis  cylinders  (amakrine  cells).  Some  of  the  nerve 
fibers  are  derived  from  the  mitral  cells,  some  from  the  molecular 
layer,  and  others  from  the  outside.  The  deeper  bundles  enclose 
granule  and  stellate  cells. 


490 


PRACTICAL  HISTOLOGY 


THE  HYPOPHYSIS 

The  hypophysis,  or  pituitary  body,  is  a  small  organ  that  lies  in  the 
sella  turcica  of  the  sphenoid  bone  and  is  connected  to  the  infundib- 
ulum  of  the  diencephalon  by  a  delicate  stalk.  It  consists  of  three 
portions,  the  anterior,  posterior  and  intermediate  portions.  These 
are  surrounded  by  a  common  capsule  of  white  fibrous  tissue  which  is 
continuous  with  the  tissue  of  the  dura.  The  complete  removal  of 
the  organ  is  said  to  be  followed  by  death  in  a  few  days. 


Fig.  274. — Section  of  Hypophysis  showing  its  Epithelial  (Left)  and 
Neural  (Right)  Lobes  with  the  Cleft-like  Pars  Intermedia  between. 
(Photograph.     Obj.  32  mm.,  oc.     7.5  X.) 

The  pars  anterior,  or  epithelial  lobe,  consists  of  epithelial  cells 
arranged  in  groups  or  chains;  the  latter  are  almost  tubular  in  form. 
These  cells  are  of  three  varieties:  clear,  acidophilic  and  basophilic 
elements.  The  clear  cells  consist  of  clear  cytoplasm  which  is  slightly 
granular.  The  nuclei  are  large  and  stain  well.  In  the  other  cells 
the  cytoplasm  contains  coarse  granules  but  the  nuclei  are  the  same. 
On  the  one  hand  the  granules  respond  to  the  plasmatic  stains  and  on 
the  other  to  the  basic  stains,  hence  acidophilic  and  basophilic  cells. 
The  latter  are  the  more  numerous.  A  small  lumen' may  be  noted 
within  the  cell  groups.  The  capillaries  are  in  close  relation  with  the 
epithelial  cells- as  in  other  glands  of  internal  secretion.     The  nerves 


THE   NERVE    SYSTEM 


491 


of  this  lobe  consist  of  a  very  few  fibers  with  numerous  branchlets 
and  ramifications  that  follow  the  arteries  and  are  distributed  mainly 
to  the  epithelial  cells.  Here  they  terminate  in  ball-like  enlargements. 
The  pars  intermedia  occupies  the  interval  that  is  represented  by 
a  cleft  between  the  two  main" lobes,  in  lower  animals.  The  epithelial 
cells  are  smaller  and  less  granular.     The  cells  of  its  anterior  area 


Fig.  275. — Section  of  the  Epithelial  Lobe  of  the  Hypophysis. 
The  large  dark  cells  are  the  basophils;  The  large  lighter  cells  are  the  acidophils; 
the    smaller  light   cells   are  the   clear   cells.     (Photograph.     Ob j. £4 .mm., 
oc.  5  X.) 

are  flattened  while  those  of  its  posterior  area  are  columnar  in  shape. 
Various-sized  masses  of  colloid,  or  hyalin  material  are  found  here. 
This  is  not  true  colloid  substance  as  is  formed  in  the  thyreoid  body 
as  it  contains  no  iodin.  It  is  derived  from  the  cells  of  the  pars 
intermedia  and  like  the  cytoplasm  of  these  cells  it  contains  glycogen. 
The  pars  nervosa  consists  chiefly  of  neuroglia  and  a  few  nerve 
fibers  that  terminate  in  the  epithelial  portions.     The  glial  cells 'may 


492  PRACTICAL   HISTOLOGY 

contain  pigment  that  is  of  a  lipoid  nature.  Hyalin  substance  is 
found  in  this  lobe  most  abundant  near  the  pars  intermedia.  It 
may  extend  into  the  infundibular  cavity  on  its  way  to  the  third 
ventricle.  This  hyalin  substance  comes  from  the  pars  intermedia 
and  seems  to  be  sent  to  the  cerebrospinal  fluid  via  the  third  ventricle. 

The  arteries  reach  the  organ  by  means  of  the  infundibulum.  As 
they  reach  the  pars  intermedia  branches  pass  to  the  pars  anterior 
and  form  plexuses  around  the  cell  groups.  The  capillaries  are  most 
numerous  in  the  pars  anterior  and  are  of  the  sinusoidal  type.  The 
veins  have  a  corresponding  course. 

The  lymph  spaces  are  numerous.  In  the  pars  anterior  they  sur- 
round the  epithelial  cells  and  lead  to  the  subarachnoid  space  and  the 
perivascular  lymph  spaces  of  the  base  of  the  brain.  As  mentioned 
previously  the  lymph  spaces  of  the  pars  nervosa  and  intermedia 
seem  to  communicate  with  the  third  ventricle. 

,  THE  EPIPHYSIS 

The  epiphysis,  or  pineal  body,  is  a  small,  apparently  unimportant 
organ  in  man.  In  some  lower  animals,  it  is  a  visual  organ.  This 
rudimentary  structure  consists  of  a  number  of  tubules  lined  by 
polygonal  cells  supported  by  fibrous  tissue  and  neuroglia  in  the  lower 
part.  These  tubules  contain  the  brain  sand,  or  acervulus  cerebri, 
peculiar  concretions  of  phosphate  and  carbonate  of  magnesium, 
ammonium  and  calcium,  which  are  not  limited  to  this  body,  how- 
ever, but  may  be  found  in  other  portions  of  the  nerve  system. 

The  circulation  of  the  nerve  system  is  carried  on  chiefly  by  the 
vessels  in  the  pia.  In  the  cerebrum,  the  vessels  of  the  cortex  enter 
vertically,  and  form  a  close  plexus  of  capillaries  most  plentiful  where 
the  cells  are.  Those  intended  for  the  medulla  are  larger,  and, 
passing  through  the  cortex,  form  capillary  networks  between  the 
fibers  and  parallel  to  them.  Other  branches  supply  the  basal 
ganglia. 

In  the  cerebellum,  the  capillaries  are  few  in  the  outer  portion  of 
the  molecular  layer,  but  in  the  granule  layer  and  around  the  cells 
of  Purkinje,  close  meshes  are  formed. 

In  the  spinal  cord,  there  are  two  sets  of  vessels,  those  that  enter 


THE   NERVE   SYSTEM  493 

at  all  points  of  the  periphery  and  supply  chiefly  the  white  matter, 
and  those  derived  from  the  artery  lying  in  the  ventromedian  fissure; 
the  latter  set  goes  to  the  gray  substance.  The  smaller  peripheral 
vessels  remain  in  the  white  substance,  and  run  parallel  to  the  fibers, 
while  the  larger  penetrate  the  gray  substance  and  supply  the  outer 
part.  The  artery  in  the  fissure  sends  branches  into  the  gray  com- 
missure; these  divide  right  and  left,  and  form  dense  plexuses  in  the 
gray  substance.  The  arteries  of  the  spinal  cord  are  terminal  as 
their  capillaries  do  not  anastomose. 

The  blood  is  collected  by  venous  radicals  that  have  the  same 
general  course.  Those  of  the  brain  empty  into  the  large  venous 
sinuses  of  the  dura.  In  the  spinal  cord  they  form  the  large  ventral 
and  dorsal  median  veins. 

Lymph  vessels  are  absent  in  the  brain  and  spinal  cord.  Lymph 
spaces,  pericellular  and  perivascular  are  very  numerous  and  com- 
municate with  the  subarachnoidean  lymph  space.  The  subarach- 
noidean  lymph  space  continues  as  the  perivascular  lymphatics  that 
accompany  the  blood-vessels. 


CHAPTER  XVIII 
THE  EYEBALL  AND  LACRIMAL  SYSTEM 

The  eyeball  (bulbus  oculi)  is  one  of  the  most  important  organs  of  the 
special  senses.  The  eyeball  occupies  the  anterior  portion  of  the 
orbital  fossa  and  is  protected  by  the  orbital  margins  and  the  eyelids. 
The  anteroposterior  and  transverse  diameters  are  24  mm.  while  the 
vertical  dimension  is  23.5  mm.  so  that  the  eyeball  is  not  quite  a 
sphere  at  the  equator.  At  birth  the  eyeball  is  about  17.5  mm.  in 
diameter  and  is  nearly  spherical  in  shape.  It  increases  about  3  mm. 
between  birth  and  puberty  and  soon  thereafter  attains  its  adult 
shape  and  size. 

The  apparent  difference  in  the  size  of  the  eyeballs  of  different 
individuals  is  not  due  to  a  real  difference  in  size  but  to  a  difference 
in  prominence  of  the  eyeball  and  width  of  the  palpebral  fissure. 
When  viewed  from  the  side  the  eyeball  is  seen  to  consist  of  parts 
of  two  spheres.  The  smaller,  anterior  corneal  portion  (about  one- 
sixth)  represents  part  of  a  sphere  of  14  mm.  diameter,  while  the  larger 
posterior  portion  (five-sixths)  represents  the  greater  part  of  a  sphere 
of  24  mm.  diameter.  The  optic  axis  is  represented  by  a  line  con- 
necting the  anterior  and  posterior  poles,  that  is  the  central  points 
of  anterior  and  posterior  curvatures,  respectively.  The  equator  is 
the  line  around  the  eyeball  midway  between  the  poles.  The  visual 
axis  is  a  line  that  passes  from  the  first  nodal  point  of  the  cornea  to 
the  fovea  centralis  of  the  retina. 

The  eyeball  is  called  the  organ  of  vision  (organon  visus).  In 
reality  it  makes  an  image  like  a  camera,  while  nerve  impulses  that 
are  generated  by  the  cells  of  the  retina  travel  to  the  brain  and  these 
impulses  are  then  translated  into  photic  impressions. 

The  eyeball  is  operated  by  a  number  of  extrinsic  muscles  that 
are  of  the  voluntary  striated  variety.  Within  the  eyeball  are  some 
smooth,  intrinsic  muscles  that  are  concerned  with  the  actions  of  the 
iris  and  the  process  of  accommodation. 

494 


THE  EYEBALL  AND   LACRIMAL  SYSTEM  495 

The  eyeball  alone  does  not  occupy  the  entire  orbit  but  addition 
the  extrinsic  muscles,  orbital  fat,  capsule  of  Tenon,  vessels  and 
nerves  are  found  here.  The  orbital  fat  forms  a  soft  bed  or  cushion 
for  the  eyeball  and  the  quantity  differs  in  various  individuals. 
If  it  is  above  the  average  amount  the  eyeballs  protrude  somewhat; 
if  it  is  less  than  the  average  condition  then  the  eyeballs  have  a  sunken 
appearance.  This  is  especially  noticeable  after  a  long  illness  and  the 
sunken  appearance  is  due  to  the  fact  that  some  of  the  fat  here  has 
been  used  as  food.     During  convalescence  the  fat  is  restored. 

The  capsule  of  Tenon  (fascia  bulbi)  is  a  lymph  space,  or  bursa 
within  which  the  eyeball  moves  as  free  from  friction  as  possible. 
This  lies  behind  the  equator  of  the  eyeball  and  consists  of  a  double 
layer  of  a  serous  membrane  which  are  continuous  with  each  other. 
This  covers  the  posterior  portion  of  the  eyeball  and  extends  as  far 
forward  as  the  reflection  of  the  conjunctiva.  The  layers  are  prac- 
tically in  apposition  and  are  pierced  posteriorly  by  the  optic  nerve 
and  is  continued  thereon.  It  is  likewise  pierced  further  forward  by 
the  tendons  of  the  ocular  muscles  and  is  prolonged  upon  each  as  a 
tubular  sheath.  That  portion  of  the  fascia  under  the  eyeball  is 
formed  like  a  swing,  or  hammock  and  seems  to  support  the  eyeball; 
it  has  therefore  been  called  the  suspensory  ligament. 

The  eyeball  is  composed  of  three  coats  and  contains  four  refrac- 
tive media.  The  coats  are  the  external,  or  c orneo -sclera ;  the 
middle,  or  choroid,  ciliary  body  and  iris;  and  the  internal,  or 
retina. 

The  refractive  media  are  the  cornea,  the  aqueous  and  vitreous 
humors  and  the  lens.  Of  these,  the  cornea  and  lens  alone  are  of 
importance. 

The  corneo-sclera  is  the  protective  and  transparent  coat  of  the 
eyeball. 

The  sclera  constitutes  about  five-sixths  of  this  coat.  It  is  com- 
posed of  coarse  bundles  of  white  fibrous  tissue  that  interlace  to 
form  a  dense,  tough  coat.  These  bundles  although  arranged  chiefly 
longitudinally  and  transversely  interlace  somewhat.  Between  the 
bundles  are  spaces  that  contain  large,  stellate  cells.  These  spaces 
communicate  with  the  lymph  spaces  within  the  cornea.  On  its 
external  surface,  the  sclera  is  in  relation  with  the  capsule  of  Tenon, 


496 


PRACTICAL   HISTOLOGY 


and,  anteriorly,  the  conjunctiva.     To  it  are  attached  the  ocular 
muscles. 

The  visible  portion  of  the  sclera  constitutes  the  white  of  the  eye; 
in  the  young  it  may  be  bluish  in  color,  in  the  adult  it  is  white,  while 
in  old  age  it  may  show  yellowish  patches. 


Fig.  276. — Section  of  the  Human  Cornea  Showing  the  Various  Layers. 
(Photograph.      Obj.   16  mm.,   oc.   7.5  X.) 

Between  the  sclera  and  the  choroid  there  is  a  lymph  space  called 
the  subscleral  space.  Here  the  tissue  is  loosely  arranged  and  the 
spaces  formed  are  lined  with  endothelial  cells.  This  reticular 
membrane  may  be  separated  from  the  sclera  except  in  the  region  of 


THE   EYEBALL   AND    LACRIMAL   SYSTEM  497 

the  optic  nerve  exit.  The  connective  tissue  cells  contain  a  brownish 
pigment  and  this  membrane  is  called  the  lamina  fusca.  At  the  exit 
of  the  optic  nerve  the  sclera  is  pierced  by  a  number  of  small  openings 
through  which  the  fila  of  the  optic  nerve  pass;  this  forms  a  sieve -like 
area  in  the  sclera  and  is  called  the  lamina  cribrosa.  At  this  region 
the  sclera  is  thickest.  Pigmentation  of  the  cells  occurs  here  as  well 
as  at  the  corneoscleral  junction. 

The  cornea  is  a  specialized  portion  of  the  sclera  modified  for  the 
transmission  of  light.  It  is  practically  a  convavoconxex  lens  with 
the  convex  side  externally  placed.  It  is  about  i  mm.  in  thickness. 
The  posterior,  or  internal  surface  is  more  extensive  than  the  anterior 
as  the  transition  from  cornea  to  sclera  begins  sooner  on  the  external 
surface.  It  consists  of  five  layers:  anterior  epithelium,  anterior 
limiting  membrane,  substantia  propria,  posterior  limiting  membrane, 
and  posterior  endothelium. 

The  anterior  epithelium  is  a  continuation  of  the  epithelium  of  the 
conjunctiva.  This  is  of  the  stratified  squamous  variety,  and  the 
tunica  propria  beneath  is  not  papillated.  The  layers  of  cells, 
usually  five  or  six,  are  more  numerous  at  the  corneo-scleral  junction 
than  in  the  center.  The  basal  cells  are  long  and  columnar,  and 
possess  processes  that  extend  into  the  anterior  elastic  lamina,  while 
the  external  cells  are  squamous.  The  middle  layers  are  prickle- 
cells,  and  the  spaces  between  are  lymph  channels.  Sensor  nerve 
fibers  are  numerous  in  the  epithelial  layers. 

The  anterior  elastic  lamina,  or  Bowman's  membrane,  is  a  clear 
prominent  band  serving  as  a  basement  membrane  to  the  epithelial 
cells.  Although  called  elastic  it  does  not  consist  of  elastic  tissue. 
It  is  thickest  in  the  center  of  the  cornea  and  becomes  thinner  as  the 
corneoscleral  junction  is  approached,  where  it  continues  as  the  thin 
basement  membrane  of  the  conjunctiva.  It  is  unusually  prominent 
for  a  basement  membrane  and  because,  like  elastic  tissue,  it  does 
not  respond  to  the  ordinary  stains  the  older  observers  were  lead  to 
believe  that  it  consisted  of  elastic  tissue.  It  does  not  respond  to 
the  elastica  stains. 

The  substantia  propria  forms  the  bulk  of  the  cornea,  and  consists 
of  a  number  of  layers  (about  sixty)  of  white  fibrous  tissue  arranged 
parallel  to  one  another.     It  is  due  to  this  arrangement  that  this 

32 


498  PRACTICAL  HISTOLOGY 

organ  is  transparent.  In  the  center  of  the  cornea  the  bundles  of 
fibers  of  the  successive  layers  cross  one  another  at  right  angles.  In 
addition  to  these  fibers,  there  are  others  that  penetrate  the  organ  at 
a  right  angle  to  the  layers,  and  bind  all  together.  These  are  the 
perforating  fibers.  Between  the  various  layers  are  a  large  number  of 
irregular  spaces  called  the  corneal  lacunae.  These  contain  large 
stellate  cells  that  are  the  original  connective-tissue  cells  of  the  organ. 
They  are  the  corneal  corpuscles.  The  spaces  communicate  with 
one  another  by  means  of  little  canals  called  canaliculi,  into  which 
their  processes  extend.  These  spaces  are  readily  shown  by  the  gold 
chlorid  method  of  staining. 

The  posterior  limiting  membrane,  or  membrane  of  Descemet, 
is  analogous  to  the  anterior  membrane;  unlike  this  one,  however,  it 
is  thicker  peripherally  than  centrally,  and  seems  more  independent 
of  the  substantia  propria  than  the  anterior.  It  does  not  respond  to- 
the  elastica  stain,  and,  consequently,  is  not  made  up  of  elastic  tissue, 
as  its  name  would  seem  to  indicate.  It  becomes  the  pectinate 
ligament.  According  to  Stohr  the  pectinate  ligament  consists  of 
fibers  passing  from  the  iris  to  the  cornea.  It  is  said  to  prevent  the 
passage  of  lymph  from  the  anterior  chamber  to  the  corneal  spaces. 

The  endothelial  layer  consists  of  a  single  layer  of  well-defined 
regular  cells,  which  cover  the  posterior  surface  of  this  organ,  and 
continue  over  the  anterior  surface  of  the  iris.  These  cells  are 
hexagonal,  and  possess  a  fibrillar  cytoplasm  that  seems  to  extend 
through  several  layers. 

The  cornea  possesses  blood-vessels  during  the  developmental  period. 
These,  however,  disappear  before  birth,  so  that  none  are  then  present. 
Lymph,  which  circulates  through  the  many  large  spaces  and  can- 
aliculi, nourishes  the  cornea.    Lymphatic  vessels  are  absent. 

The  sclera  possesses  but  few  vessels,  and  these  are  found  chiefly 
at  the  corneo-scleral  junction,  where  a  circular  network  is  formed. 
They  anastomose  with  the  vessels  of  the  choroid. 

The  nerves  are  sensor \  at  the  corneo-scleral  junction  a  circular 
plexus  is  formed,  from  which  fibers  pass  into  the  substantia  propria, 
while  others  penetrate  the  anterior  elastic  lamina  to  pass  into  the 
epithelial  layer.  Some  of  these  fibers  extend  almost  to  the  surface. 
Bulbs  or  corpuscles  occur  near  the  scleral  margin  of  the  cornea. 


THE    EYEBALL   AND    LACRIMAL   SYSTEM 


499 


The  middle  coat,  or  tunic,  also  called  the  uveal  tract,  is  the 
vascular  coat.  It  contains  the  main  vessels  of  the  eyeball,  except 
the  central  artery  of  the  retina,  and  consists  of  the  choroid,  ciliary 
body  and  iris. 

The  choroid  is  the  vascular  portion,  and  is  divided  into  three 
layers,  the  stroma  layer,  the  choriocapillaris,  and  the  glassy 
membrane,  from  without,  inward. 


Cross  and  longitudinal 
sections  of  bundles 
of  scleral  fibers. 

Lamina  supra- 
chorioidea. 


)    Lamina  vasculosa. 


Boundary  zone. 
Choriocapillaris. 
Basal  membrane. 
Pigment  layer  of  the 
retina. 

Fig.  277. — Vertical  Section  through  a  Part  of  the  Human  Sclera  and 

the  Entire  Thickness  of  the  Choroid.     X  100.     (Lewis  and  Slohr.) 

g.  Large  vessels;  p,   pigment  cells;  c.   cross-section  of  capillaries. 


The  stroma  layer  is  sometimes  referred  to  as  the  layer  of  large 
vessels,  as  they  are  found  only  in  this  portion.  It  consists,  ex- 
ternally, of  delicate  fibers  that  connect  with  those  of  the  sub- 
scleral  tissue  and  form  a  complete  space,  the  suprachoroidal, 
or  subscleral  lymph  space.  In  this  tissue  are  found  pigmented 
connective-tissue  cells,  and  it  has  received  the  name  of  lamina 
suprachoroidea.  This  consists  of  a  delicate  meshwork  of  fibers 
some  of  which  pass  to  the  lamina  fusca  of  the  sclera  and  others  to  the 
stroma  layer  of  the  choroid.     Pigmented  connective  tissue  cells  are 


500  PRACTICAL   HISTOLOGY 

numerous;  they  may  be  scattered  or  in  groups.  Their  cytoplasm 
contains  coarse  brownish  granules  of  pigment.  The  main  portion 
of  the  stroma  layer  consists  of  bundles  that  are  closely  arranged. 
The  networks  formed  by  these  are  the  venous  trunks,  externally, 
and  the  arterial  trunks,  internally;  the  latter  are  accompanied  by 
bundles  of  smooth  muscle  tissue.  Pigmented  cells  exist  between 
the  bundles. 

The  inner  portion  of  this  layer  is  a  narrow  dense  zone  and  is 
called  the  boundary  zone;  the  bundles  are  arranged  into  several 
layers  in  herbivorous  animals,  so  as  to  give  a  peculiar  metallic 
reflex,  and  constitute  the  tapetum  fibrosum.  This  area  is  usually 
free  from  pigment  cells.  In  the  carnivorous  animals  the  fibers  are 
replaced  by  distinct  cells  that  contain  crystals.  The  metallic  reflex, 
however,  is  the  same.     This  forms  the  tapetum  cellulosum. 

The  choriocapillaiis  contains  little  stroma,  and  is  composed 
chiefly  of  a  dense  capillary  plexus.  No  pigment  cells  are  seen. 
The  capillaries  are  most  numerous  around  the  macula  latea. 

The  glassy  membrane  or  membrane  of  Bruch,  lies  at  the  inner 
boundary  of  the  choroid,  and  consists  of  refractile,  homogeneous 
tissue.  It  is  a  very  thick  basement  membrane,  and  supports  the 
pigmented  cells  of  the  retina,  which  form  small  depressions  in  its 
surface.     This  membrane  increases  in  thickness  in  old  age. 

The  choroid  extends  to  the  ora  serrata,  a  peculiar,  serrated  line, 
at  which  the  neural  portion  of  the  retina  ceases.  At  this  point, 
the  choroid  continues  as  the  ciliary  body. 

The  ciliary  body  is  composed  of  three  main  portions,  the  ciliary 
ring,  the  ciliary  processes  and  the  ciliary  muscle.  It  is  thicker 
than  the  choroid,  which  is  due  especially  to  the  addition  of  the 
muscle  tissue. 

The  ciliary  ring  is  practically  the  continuation  of  the  stroma  layer 
of  the  choroid  and  the  glassy  membrane,  and  consists  of  dense 
white  fibrous  tissue,  which  forms  a  circular  band  about  4  mm.  in 
breadth.  The  outer  bundles  mix  with  the  bundles  of  fibers  of  the 
ciliary  muscle.     The  vessels  have  a  longitudinal  course. 

The  ciliary  processes  are  projections  of  the  stroma,  covered  by 
pigmented  epithelial  cells,  from  60  to  80  in  number.  They  arise 
at  the  junction  with  the  choroid,  and  extend  toward  the  iris,  in- 


THE   EYEBALL   AND   LACRIMAL   SYSTEM 


50I 


creasing  in  height,  ending  abruptly  at  that  point.  At  this  place 
they  are  about  1  mm.  in  height.  Each  process  consists  of  a  core 
of  stroma  (connective  tissue)  supporting  blood-vessels  and  covered 
by  the  pigmented  epithelial  cells  of  the  retina,  the  pars  ciliaris 
retinae.  This  is  said  to  be  the  most  vascular  region  of  the  eyeball. 
These  cells  rest  upon  a  continuation  of  the  glassy  membrane.  There 
are  two  layers,  the  outer,  or  basal  of  which  consists  of  low  columnar 
or  cuboidal  elements  that  are  the  continuation  of  the  true  pigmented 


Corneal  epithe- 
lium. 

Substantia  pro- 
pria. 


Descemet's 
membrane. 

Canal  of 
Schlemm. 


Loose  connec- 
tive tissue  of 
the  conjunc- 
tiva. 


Conjunctiva. 


Iris. 
Pigment  layer. 


Meridional  fibers. 
Radial  fibers. 
Miiller's  fibers. 


Processus  ciliares. 
Fig.  278. — Meridional    Section    of    the    Human    Ciliary 

(Bohm,  Davidoff  and  Huber.) 


Body.     X  20. 


cells  of  the  retina.  The  cytoplasm  is  usually  filled  with  brownish 
pigment  granules  but  the  nucleus  is  not  invaded.  The  inner  layer 
is  composed  of  cells  that  are  columnar,  possess  little  or  no  pigment. 
The  cytoplasm  is  usually  clear  or  only  slightly  granular  and  may 
show  fibrillation  or  contain  delicate  rods.  These  cells  are  the  repre- 
sentative of  the  optical  portion  of  the  retina.  In  places  gland-like 
evaginations  of  the  pigmented  epithelium  are  noted.  These  are 
the  so-called  ciliary  glands. 

The  ciliary  muscle  is  of  the  nonstriated  variety,  and  lies  external 
to  the  ciliary  ring,  just  beneath  the  sclera.  The  fibers  are  arranged 
in  meridional,  radial  and  circular  sets.  The  meridional  are  the 
outermost,  and  extend  from  the  canal  of  Schlemm,  in  the  corneo- 
scleral junction,  to  the  ciliary  ring.     The  fasciculi  vary  in  length 


502  PRACTICAL   HISTOLOGY 

and  represent  the  bulk  of  the  ciliary  muscle.  These  are  the  tensor 
muscles  of  the  choroid.  The  radial  fibers,  which  compose  the  middle 
layer,  extend  peripherally,  and,  spreading  fan-like,  are  inserted  into 
the  ciliary  ring  and  processes.  These  fibers  are  less  numerous 
and  run  a  shorter  course.  Although  they  start  out  like  the  meridi- 
onal fibers  they  soon  are  arranged  parallel  to  the  radii  of  the  eyeball. 
The  circular  fibers  are  the  inner  ones,  and  their  direction  is  equatorial. 
The  fibers  are  arranged  in  small  bundles  that  are  mixed  with  the 
radial  fibers  and  pectinate  ligament.  These  fibers  are  said  to  be 
increased  in  number  in  hypermetropic  eyes  and  reduced  or  absent 
in  myopic  eyes.  They  constitute  Miiller's  ring-muscle.  The  cili- 
ary muscle  is  important  in  the  process  of  accommodation. 

The  ciliary  region  is  indicated,  externally,  by  a  band  about  one- 
fourth  of  an  inch  broad,  starting  at  the  corneoscleral  junction.  It 
is  called  the  clanger  zone  of  the  eyeball,  as  injuries  here  usually 
result  fatally  to  sight. 

The  iris  is  the  continuation  of  the  stroma  layer  and  glassy  mem- 
brane of  the  choroid.  It  receives  also  the  posterior  lamina  and  the 
endothelium  of  the  cornea,  and  consists  of  the  anterior  endothelium, 
stroma  layer,  posterior  lamina  and  pigment  layers. 

The  anterior  endothelium  is  a  continuation  of  that  of  the  cornea, 
and  covers  the  anterior  surface  of  the  iris.  The  cells  are  neither 
so  regular  nor  distinct  as  those  of  the  cornea.  In  areas  they  are 
wanting  and  permit  of  a  direct  communication  between  the  inter- 
cellular spaces  of  the  iris  with  the  anterior  chamber. 

The  stroma  layer  is  composed  chiefly  of  a  coarse  network  of  white 
fibrous  tissue,  some  of  which  is  circularly  arranged  around  the  blood- 
vessels, which  possess  no  muscular  coat.  Anteriorly,  this  stroma 
is  very  much  reticulated  and  forms  a  support  for  the  endothelial 
cells.  According  to  some  authors,  this  portion  constitutes  an  ante- 
rior limiting  membrane.  The  connective  tissue  cells  are  unusually 
numerous.  In  the  stroma  layer,  pigment  cells  are  found  in  varying 
quantities;  in  gray  eyes,  very  few  are  seen;  as  the  color  passes  to 
blue,  brown  and  black,  the  number  increases,  the  last  possessing 
the  most.  In  albino  eyes  not  only  are  the  pigmented  connective 
cells  of  the  stroma  layer  absent,  but  the  pigment  that  is  usually 
present  in  the  posterior  epithelial  cells  continued  from  the  retina 


THE  EYEBALL  AND   LACRIMAL   SYSTEM  503 

is  also  absent.  As  a  result  of  this,  the  retinal  blood-vessels  cause 
a  peculiar  red  reflex,  the  retinal  reflex.  In  the  other  eyes  the  pig- 
ment obscures  it. 

The  stroma  is  quite  vascular;  the  large  vessels  have  a  meridional 
direction.  These  vessels  usually  produce  slight  ridges  upon  the 
anterior  surface  of  the  iris  and  between  these  are  slight  grooves. 
The  anterior  surface  has  therefore  an  uneven  appearance. 

In  the  stroma  is  found  muscle  tissue  of  the  involuntary  nonstriated 
variety.  This  is  arranged  circularly  and  radially.  The  circular 
fibers  are  near  the  anterior  part  of  the  iris,  and  contract  the  pupillary 
aperture  when  stimulated;  these  form  the  sphincter  pupillae  muscle. 
The  radial  fibers  lie  near  the  posterior  part,  and  when  they  contract, 
the  pupillary  aperture  is  dilated;  they  constitute  the  dilatator 
pupillae  muscle.  According  to  Schafer  this  muscle  covers  the  poste- 
rior surface  of  the  iris  stroma  as  a  single  layer  of  thin,  flat  cells.  At 
the  periphery  of  the  iris  is  two  to  three  cells  thick.  No  basement 
membrane  intervenes  between  this  muscle  and  the  pars  iridica 
retinae. 

The  posterior  limiting  membrane,  or  membrane  of  Bruch,  is  a 
continuation  of  the  glassy  membrane.  It  supports  the  pigmented 
cells,  the  pars  iridica  retinae. 

The  pigmented  layer,  a  continuation  of  the  pars  ciliaris  retinae, 
and  called  the  pars  iridica  retinae,  is  usually  pigmented,  and  consists 
of  two  layers  of  cells.  The  cells  are  filled  with  pigment  and  with 
adults  the  individual  elements  cannot  be  distinguished.  It  con- 
tinues to  the  anterior  margin  of  the  pupil. 

The  pupil  is  the  aperture  in  the  iris.  Its  size  is  regulated  auto- 
matically by  the  amount  of  light  entering. 

The  iris  is  an  automatic  curtain  that  is  suspended  in  the  aqueous 
humor.  It  regulates  the  amount  of  light  that  enters  the  lens  and 
divides  the  anterior  and  posterior  chambers  from  each  other. 

The  corneoscleral  junction  is  the  region  in  which  cornea,  sclera, 
ciliary,  body  and  iris  come  together.  The  sclera  passes  over  into 
the  cornea,  but  the  line  of  transition  is  not  abrupt,  but  gradual, 
and  forms  an  oblique  line  that  extends  from  before,  backward 
and  inward  so  that  the  posterior  surface  of  the  cornea  is  greater 
in  extent  than  the  anterior  surface.     Beneath  the  posterior  margin, 


5°4 


PRACTICAL   HISTOLOGY 


usually  within  the  sclera,  is  a  circular  canal,  the  canal  of  Schlemm, 
which  extends  around  the  corneoscleral  junction.  Through  this 
canal  the  lymph  of  the  cornea,  spaces  of  Fontana  and  anterior 
chamber  enters  the  scleral  venules.  In  this  region,  the  membrane 
of  Descemet  is  seen  to  divide  into  a  large  number  of  fibers  that 
extend  to  the  base  of  the  iris.  Some  of  the  ciliary  muscle  fibers 
arise  here  and  assist  in  forming  a  network.  Between  the  fibers  are 
found  many  intercommunicating  spaces  called  the  spaces  of  Fontana. 


Fig.  279. — Corneoscleral  Junction  of  Max. 
1,  Epithelium;  2,  connective  tissue  of  conjunctiva;  3,  sclera;  4,  5,  6,  7  and  8, 
ciliary  body;  4,  meridional;  5,  radial;  6,  circular  fibers  of  ciliary  muscle; 
7,  ciliary  process;  8,  pars  ciliaris  retinae;  9,  pars  iridica  retinae;  10,  stroma 
of  iris;  11,  posterior  elastic  lamina  of  cornea;  12.  substantia  propria;  13, 
epithelium;  14,  canal  of  Schlemm;  15,  angle  of  iris,  or  infiltration  angle. 
(Stohr's  Histology.) 

These  spaces  lie  around  the  angle  formed  by  the  cornea  and  iris, 
called  the  infiltration  angle,  and  communicate  with  the  anterior 
chamber  and  the  canal  of  Schlemm.  The  network  is  called  the 
pectinate  ligament,  and  is  covered  by  endothelial  cells.  It  is  more 
prominent  in  some  lower  animals  than  in  man. 

THE  RETINA 

The  retina  forms  the  internal,  or  neural  coat  of  the  eyeball.  It 
may  be*  divided  into  two  portions,  the  pars  optica,  that  portion 
capable  of  vision,  and  the  pars  ceca,  or  the  blind  part,  possessing 


THE   EYEBALL   AND    LACRIMAL   SYSTEM  505 

no  nerve  elements.  The  latter  portion  is  further  subdivided  into 
pars  cHiaris  and  pars  iridica  retinae.  The  simplest  division  of  the 
retina,  however,  is  pars  optica,  pars  ciliaris  and  pars  iridica  retinae. 

The  pars  optica  lines  almost  the  entire  optic  cup,  and  extends 
forward  to  the  end  of  the  choroid.  Here  the  neural  portion  ceases, 
and  the  coat  becomes  abruptly  thinner,  and  forms  an  irregular 
serrated  line,  the  ora  serrata.  From  this  point,  the  last  two  por- 
tions of  the  retina  continue. 

The  optical  portion  consists  of  eleven  layers,  counting  the  pig- 
mented layer.  These  layers  are  classed  as  neuro -epithelial  and 
cerebral.  The  neuro -epithelial  portion  consists  of  the  first  layers 
within  the  pigment  layer,  and  the  cerebral  portion  the  remaining 
divisions.  The  pigmented  part  is  derived  from  the  outer  layer  of 
the  optic  cup,  and  the  other  parts  from  the  inner  layer. 

Optic  Vesicle  Retinal  Layer  Classes 

1.  Outer  Layer.  Pigmented  Layer.  PIGMENT  LAYER. 

'  Layer  of  rods  and  cones. 
External  limiting 

membrane NEURO -EPITHELIAL     LAYER. 

Outer    granular    layer. 

HeNLE's     FD3ER     LAYER. 

Outer  reticular  (molecular). 
Outer  ganglionic  (inner  granule). 
Inner  reticular 

(molecular)....  CEREBRAL. 
Inner  ganglionic. 
Nerve  Fibers. 
Internal  limiting  membrane. 

1.  The  pigment  layer  of  the  retina  consists  of  a  single  layer  of 
polyhedral  cells  that  contain  a  black,  granular,  mobile  pigment 
(Justin).  The  position  occupied  by  this  pigment  depends  upon 
whether  the  eyeball  was  fixed  in  or  during  the  exclusion  of  light. 
The  cells  possess  some  processes  that  extend  around  the  bodies  of 
the  rod  and  cone  cells.  If  the  eyeball  is  fixed  in  the  presence  of 
light  the  pigment  granules  seem  to  collect  in  these  processes  while 
the  remainder  of  the  cytoplasm  is  practically  free.  If  the  eyeball 
be  removed  and  fixed  in  the  dark  the  pigment  granules  lie  in  the 


2.  Inner  Layer. 


506 


PRACTICAL  HISTOLOGY 


body  of  the  cell.  The  micleus  occupies  that  portion  of  the  cell 
near  the  basement  membrane  (glassy  membrane  of  the  choroid) 
and  is  devoid  of  these  pigment  granules.  These  pigment  granules 
apparently  absorb  the  excess  rays  of  light  and  convert  them  into 


Fig.  280. — Section  of  Human  Retina.     {After  Pier  sol.) 
A,  Part  of  pigment  layer;  B,  layer  of  rods  and  cones;  C,  external  limiting  mem- 
brane; D,  (outer)  nuclear  layer;  E,  outer  reticular  layer;  F,  outer  ganglionic 
layer;  G.  inner  reticular  layer;  H,  inner  ganglionic  layer;  J,  layer  of  nerve 
fibers;  K,  inner  limiting  membrane.     Henle's  fiber-layer  is  not  represented. 


heat  and  are  also  said  to  replace  the  rhodopsin  of  the  rod  cells  as  this 
become  bleached  through  the  action  of  the  light.  These  cells  con- 
tinue over  the  ciliary  body  and  iris  as  the  pars  ciliaris  and  pars 
iridica  retinae.     In  the  iris  both  layers  are  pigmented  but  not  in 


THE   EYEBALL  AND   LACRIMAL  SYSTEM  507 

the  ciliary  region.  This  layer  of  cells  is  derived  from  the  outer 
layer  of  the  optic  cup. 

The  neuro-epithelial  elements  and  the  nerve  cells  and  fibers  are 
supported  by  neuroglia,  of  which  there  is  a  great  deal  present,  but 
this  is  unevenly  distributed. 

2.  The  layer  of  rods  and  cones  is  the  most  important  of  the 
retina. 

The  cone  cells  consist  of  cone-body  and  cone-fiber.  The  cone- 
body  varies  in  length  and  consists  of  two  segments,  outer  and  inner. 
The  outer  segment  is  the  shorter,  conical  and  may  be  striated.  This 
portion  rests  upon  the  external  limiting  membrane  and  apparently 
consists  of  discs.  The  inner  segment  is  striated  and  flask-shaped. 
The  cytoplasm  of  this  portion,  at  its  junction  with  the  outer  segment, 
is  granular  while  the  remainder  is  fibrillar.  The  cone-fiber  is  the 
continuation  of  the  cell-body,  lies  within  the  internal  limiting  mem- 
brane and  passing  inward  terminates  in  the  outer  reticular  layer. 
At  its  junction  with  the  body  it  is  slightly  enlarged  {cone-foot)  and 
this  portion  contains  the  nucleus.  The  nucleus  stains  less  deeply 
than  the  nucleus  of  the  rod  cell.  The  length  of  the  cones  varies 
in  different  parts  of  the  retina.  Near  the  ora  serrata  they  are  about 
22  microns  long;  midway  between  the  ora  and  the  optic  papilla, 
31  microns;  at  the  edge  of  the  fovea  centralis,  44  microns;  in  the 
center  of  the  fovea,  88  microns.  The  cone  bodies  average  about 
35  microns  in  length  and  7  microns  in  thickness. 

The  rod  bodies  are  longer  on  the  average  than  those  of  the  cone 
cells  and  more  nearly  uniform  in  size.  They  average  about  60  microns 
in  length  and  2  microns  in  thickness.  Each  consists  of  an  outer  and 
an  inner  segment  which  react  differently  to  stains.  The  outer 
segment  does  no  respond  well  to  the  ordinary  stains  and  is  aniso- 
tropic and  is  brighter  in  appearance  than  the  inner  segment.  This 
portion  contains  the  rhodopsin,  or  visual  purple,  which  after  having 
been  bleached  by  the  action  of  light  is  rapidly  replaced  by  the 
pigment  cells  of  the  retina.  This  segment  is  said  to  be  surrounded 
by  a  delicate  neurokeratin  sheath.  The  inner  segment  is  somewhat 
spindle-shaped  and  at  the  junction  with  the  outer  segment  the 
cytoplasm  is  granular.  The  rest  of  the  cytoplasm  is  fibrillar.  The 
rod-fiber  is   the   continuation  of   the   cytoplasm  and  contains  the 


508  PRACTICAL   HISTOLOGY 

nucleus.  The  fiber  is  far  more  delicate  than  that  of  the  cone  cell, 
markedly  varicose  and  the  various  nuclei  are  at  different  levels. 
In  the  case  of  the  nuclei  of  the  cone  cells  they  are  all  placed  at  the 
same  level  and  lie  next  to  the  limiting  membrane.  The  nuclei  of  the 
rod  cells  are  far  more  numerous  than  those  of  the  cone  cells  and  so 
are  scattered  to  the  best  advantage  in  the  outer  nuclear  layer.  The 
nuclei  of  the  rod  cells  are  peculiar  in  that  the  chromatin  seems  to 
be  distributed  in  the  form  of  several  transverse  bands,  giving  the 
nucleus,  thus,  a  striated  appearance.  The  rod-fiber  terminates  in 
the  outer  reticular  layer. 


-e 


s> 


V 

1  3  4  S 

Fig.  281. — Cells  from  Retina  of  an  Ape.  (Stohr's  Histology.) 
1.  Cell  of  ganglionic  layer.  2,  Cells  of  inner  granule  layer.  3,  Rod-cells — a, 
Outer  segment;  i.  inner  segment;  k,  rod-granule;  x,  fiber  apparatus.  Be- 
low are  rod-cells  and  fragments.  4,  Cone-visual  cells — a,  Outer  segment; 
i,  inner  segment;  k,  cone-granule;/,  cone-fiber;  x,  fiber  apparatus.  5,  Radial 
fiber;  Midler's  fiber;  k,  nucleus;  r,  pyramidal  base. 

There  are  usually  three  or  four  rod  cells  to  one  cone  cell;  a  recent 
estimation  of  the  cells,  however,  would  place  the  proportion  about 
two  to  one,  i.e.,  150  million  rods  and  70  million  cones.  The  rod  and 
cone  cells  constitute  parts  of  three  layers,  the  rod  and  cone  layer  (cell 
bodies),  the  outer  nuclear  layer  (rod  and  cone-fibers  and  nuclei)  and 
a  part  of  the  outer  reticular  layer  (terminal  branches  of  the  fibers). 

The  rod  and  cone  cells  seem  to  have  different  functions.  The 
cone  cells  contain  no  rhodopsin  and  so  this  as  well  as  the  rod  cells  is 
unessential  to  sharp  vision  in  human  beings.  In  some  animals  the 
visual  purple  is  said  to  be  wanting.  In  birds  and  reptiles  it  is  said 
that  the  cones  are  more  numerous  than  the  rods  and  in  lizards  there 
are  no  rods.  In  the  owl  and  most  nocturnal  animals  the  cones  are 
very  few  in  number,  poorly  developed  or  entirely  absent.     The  cones 


THE   EYEBALL   AND   LACRIMAL   SYSTEM  509 

are  said  to  have  to  do  with  color  perception  and  in  color  blindness 
they  are  defective.  The  rods  are  concerned  with  light  perception  so 
that  in  night-blindness  these  elements  are  defective. 

3.  The  outer  limiting  membrane  is  a  part  of  the  supportive  tissue  of 
the  retina.  This  is  neuroglia  and  comprises  the  glial  cells  and  fibers. 
The  glial  cells  are  called  the  sustentacular  cells,  or  fibers  of  Miiller. 
These  are  irregular  column-shaped  elements  that  are  radially  placed 
and  extend  almost  throughout  the  entire  thickness  of  the  retina. 
Their  outer  extremities  fuse  to  form  the  outer  limiting  membrane, 
from  the  peripheral  surface  of  which  delicate  fibrillar  extend  between 
the  rod  and  cone-bodies  forming  the  rod  and  cone  sockets.  This 
outer  limiting  membrane  is  perforated  for  the  bodies  of  the  rod  and 
cone  cells.  The  inner  extremities  of  the  sustentacular  cells  fuse  to 
form  the  inner  limiting  membrane  the  most  internal  layer  of  the  retina. 
From  these  cells  of  Miiller  lateral  branches  are  given  off.  These 
assist  the  glial  fibers  in  forming  the  general  supportive  tissue  of  the 
retina.  In  the  meshwork  thus  formed  there  are  some  astrocytes  in 
the  ganglion  cell  layers. 

The  nuclear  or  granule  layer  consists  of  four  or  five  layers  of  nuclei 
that  represent  the  nuclei  of  the  rod  and  cone  cells  and  the  bulk  of  the 
fiber  processes  of  these  cells.  The  cone  nuclei  are  all  in  a  single  row 
along  the  outer  limiting  membrane  and  form  only  about  one-fourth 
of  the  thickness  of  the  layer.  The  remainder  is  made  up  of  the 
nuclei  of  the  rod  cells  that  are  scattered  throughout  the  inner  three- 
fourths  of  this  layer.  Glial  fibers  are  present  as  are  also  some  of  the 
dendritic  branches  of  some  of  the  small  cells  of  the  outer  ganglionic 
layer. 

5.  Henle's  fiber  layer  is  best  developed  in  the  macular  region  from 
which  area  it  diminishes  peripherally.  It  is  usually  considered  a 
specialized  portion  of  the  outer  reticular  layer  but  differs  from  it 
in  that  its  fibrils  are  radially  arranged  while  the  others  are  irregular. 

6.  The  outer  reticular,  or  molecular  layer  is  a  meshwork  of  fibrils 
from  different  sources.  On  the  one  hand,  the  rod  and  cone  fibers 
(really  axones)  terminate  here  in  teloneurites;  these  form  synapses 
with  the  telodendrites,  or  process  that  come  from  the  cells  of  the 
outer  ganglionic  layer  and  constitutes  the  end  of  the  first  neuron  of 
the  visual  pathway. 


5"> 


PRACTICAL  HISTOLOGY 


7.  The  outer  ganglionic,  or  inner  nuclear  layer  consists  of  several 
varieties  of  closely  packed  cells.  The  outermost  cells  are  horizon- 
tally placed.  They  are  stellate,  or  pyramidal  cells  of  two  sizes 
mainly.     The  dendrites  of  the  large  cells  pass  to  the  reticular  layer 


rf      l 


Fig.  282. — Diagram  of  the  Layers  of  the  Retina. 
I,  Layer  of  pigment  cells;  2,  rod  and  cone  bodies;  3,  inner  limiting  mem- 
brane; 4,  (outer)  nuclear  layer;  5,  6,  layer  of  Henle's  fiber  and  outer 
reticular  layer;  7,  outer  ganglionic  layer  (inner  nuclear  layer);  a,  hori- 
zontal cells;  b,  middle  layer;  c,  amakrin  cells;  8,  inner  reticular  layer; 
9,  inner  ganglionic  layer;  10,  layer  of  nerve  fibers;  e,  nerve  fiber  from  the 
brain  terminating  in  the  inner  reticular  layer  in  relation  with  the  teloneurites 
of  an  anakrin  cell;  II,  internal  limiting  membrane;  d,  sustentacular 
(Muller)  forming  the  limiting  membranes  and  general  supportive  substance 
of  the  retina. 


and  terminate  in  relation  with  the  filaments  of  the  rod-fibers.  Those 
of  the  smaller  cells  end  in  relation  with  the  filaments  of  the  cone-fibers. 
The  axones  of  both  large  and  small  cells  pass  to  the  inner  reticular 


THE   EYEBALL  AND   LACRIMAL   SYSTEM  511 

layer  where  they  form  synapses  with  the  dendritic  processes  of  the 
large  ganglion  cells.  It  is  said  that  the  smaller  cells  are  of  an 
associative  function. 

The  middle  portion  of  the  outer  ganglionic  layer  contains  the 
bipolar  cells  that  are  the  most  numerous  of  this  layer.  These  are 
placed  vertically  and  the  small  amount  of  cytoplasm  present 
continues  internally  as  an  axonic  process  that  terminates  in  the  inner 
reticular  layer  in  relation  with  the  process  (dendritic)  of  the  large 
ganglion  cells.  The  peripheral  processes  of  the  oval  cells  are  the 
dendrites  and  they  terminate  in  telodendrites  in  the  outer  reticular 
layer  in  relation  with  the  terminal  fibrils  of  the  rod  and  cone-fibers, 
forming  synapses. 

The  inner  cells  are  the  amakrin  cells  of  Cajal  and  these  form  a 
thin  zone  near  the  inner  boundary  of  the  ganglionic  layer.  These 
large  stellate  elements  send  their  dendrites  to  form  a  part  of  the 
outer  reticular  layer.  They  were  called  amakrin  cells  because  it 
was  believed  that  they  possessed  no  axones,  but  they  do.  Some  of 
these  axones  pass  to  the  inner  reticular  layer  and  terminate  in  relation 
with  the  terminal  fibrils  of  axones  that  come  from  the  brain  through 
the  optic  nerve.    Little  is  known  about  the  other  axones. 

The  nuclei  of  the  cells  of  Muller  lie  in  this  layer. 

8.  The  inner  reticular,  or  molecular  layer  consists  of  a  dense 
reticulum  of  fibrils.  These  fibrils  represent  the  teloneurites  of  the 
cells  of  the  outer  ganglionic  layer  and  of  some  of  the  axones  of  the 
fibers  of  the  optic  nerve  (centrifugal)  and  the  telodendrites  of  the 
cells  of  the  inner  ganglionic  layer.  These  fibrils  may  give  the  layer 
a  striated  appearance. 

9.  The  inner  ganglionic  layer,  or  layer  of  large  nerve  cells  is 
composed  of  a  single  layer  of  large  multipolar  ganglion  cells.  The 
cell  bodies  are  flask-shaped,  spheroidal,  or  even  stellate  and  their 
axones  form  the  greater  part  of  the  nerve  fiber  layer.  The  dendrites 
pass  peripherally  and  form  a  part  of  the  inner  reticular  layer.  In 
the  region  of  the  macula  lutea  these  cells  form  a  layer  seven  to 
eight  cells  deep;  in  the  fovea  centralis  they  are  absent. 

10.  The  layer  of  nerve  fibers  represents  the  expanded  portion  of 
the  optic  nerve.  These  fibers  arise  mainly  from  the  large  ganglion 
cells  and  are  at  first  amyelinated,    They  converge  from  all  parts 


512  PRACTICAL   HISTOLOGY 

of  the  retina  toward  the  optic  nerve  area,  or  blind  spot,  become 
myelinated  and  pass  through  the  cribriform  lamina.  By  virtue  of 
this  convergence  of  the  fibers  at  the  blind  spot  the  nerve  fiber  layer 
is  thickest  here  and  forms  a  ridge-like  elevation  at  this  region.  This 
layer  decreases  in  thickness  as  the  ora  serrata  is  approached  and  at 
this  region  ceases  entirely.  The  fibers  may  interlace  somewhat 
within  the  layer.  Some  of  the  fibers  within  this  layer  are  derived 
from  the  brain  and  carry  impulses  into  the  eyeball.  Some  of  these 
axones  terminate  in  relation  with  the  axones  of  the  amakrin  cells. 

n.  The  inner  limiting  membrane  is  a  delicate  structure  formed 
by  the  fusion  of  the  internal  extremities  of  the  cells  of  Miiller.  This 
limits  the  retina  internally  and  is  in  contact  with  the  hyaloid  mem- 
brane of  the  vitreous  humor. 

The  retina  contains  a  rich  capillary  plexus  derived  from  a  special 
vessel,  the  central  retinal  artery.  This  enters  the  eyeball  through  the 
center  of  the  optic  nerve  and  within  the  eyeball  divides  into  a 
whorl-like  set  of  vessels  from  the  center  of  the  blind  spot.  Venous 
channels  form  the  central  retinal  vein  that  passes  out  of  the  eyeball 
by  the  side  of  the  artery,  These  vessels  anastomose  with  some  of 
the  others  that  supply  the  eyeball. 

There  are  three  important  areas  in  the  retina:  (i)  the  optic  nerve 
exit,  optic  papilla,  or  blind  spot;  (2)  the  macula  lutea,  or  yellow  spot, 
and  (3)  the  ora  serrata. 

1.  In  the  blind  spot,  only  the  layer  of  nerve  fibers  is  present.  It 
lies  about  one-eight  of  an  inch  to  the  nasal  side,  and  about  one-tenth 
of  an  inch  below  the  optic  axis.  In  the  center  is  usually  a  shallow 
depression;  around  the  edge  it  is  raised  and  forms  the  papilla  nervi 
opticae. 

2.  The  yellow  spot  is  not  in  the  direct  visual  axis.  The  color  is 
due  to  the  presence  of  a  diffuse  yellow  pigment.  Its  edge  is  raised, 
owing  to  the  great  thickness  of  the  inner  ganglionic  layer.  From 
the  edge  to  the  center,  all  the  layers  decrease  and  disappear,  so  that 
in  the  center,  the  fovea  centralis,  the  cones  alone  are  present.  Here 
vision  is  most  acute. 

3.  At  the  ora  serrata  all  of  the  neural  layers  end  abruptly,  and 
are  continued  as  a  single  layer  of  cuboidal  or  columnar  cells.  Beyond 
this  point,  there  is  no  vision. 


THE    EYEBALL   AND    LACRIMAL   SYSTEM 


513 


The  light  rays  falling  upon  the  retina  are  not  transmitted  to  the 
brain  by  a  direct  route.  The  impressions  are  received  by  the  rods 
and  cones,  which  send  impulses  to  the  outer  reticular  layer  (end  of  the 
first  neuron) ;  here  the  impulses  are  received  by  the  processes  of  the 
outer  ganglionic  layer,  conveyed  through  the  bodies  of  the  cells  of 
that  layer  to  the  inner  reticular  layer  (end  of  the  second  neuron); 
here  they  are  relayed  to  the  processes  of  the  cells  of  the  inner  gangli- 


10  11 


Fig.  283. — Longitudinal  Section  of  the  Optic  Entrance  of  a  Human  Eye. 

X  15.     {Lewis  and  Stohr.) 

Above  the  lamina  cribrosa  is  seen  the  narrowing  of  the  optic  nerve,  due  to  its  loss 
of  myelin.  The  central  artery  and  vein  have  been  for  the  most  part  cut 
longitudinally,  but  above  at  several  points  transversely.  1,  Hyaloid  mem- 
brane loosened;  2,  retina;  3,  chorioid;  4,  sclera;  5,  bundles  of  the  optic 
nerve;  6,  pial  sheath;  7,  arachnoidal  sheath;  8,  dural  sheath;  9,  fibers  of 
the  lamina  cribrosa;   io,  central  artery;  11,  central  vein. 

onic  layer  and  to  its  cells  (cells  of  the  third  neuron)  and  thence  to  the 
nerve  fiber  layer;  the  latter  makes  up  the  optic  nerve  by  means  of 
which  the  impulses  are  then  conveyed  to  various  parts  of  the  brain. 
The  cell  of  the  lower  centers  (pulvinar,  corpora  quadrigemina) 
represent  the  fourth  neuron  cells  while  those  of  the  cuneus  repre- 
sent the  fifth  neurons. 

The  optic  nerve  consists  of  a  single  bundle  of  nerve  fibers  that 
33 


SM 


PRACTICAL  HISTOLOGY 


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THE  EYEBALL  AND   LACRIMAL   SYSTEM  515 

possess  no  neurilemmae.  It  is  said  to  contain  from  450,000  to 
800,000  nerve  fibers.  It  is  surrounded  by  the  dura,  arachnoid,  and 
pia,  continued  from  the  brain.  The  lymph  spaces  included  within 
these,  communicate  with  those  of  the  eyeball.  The  dura  and  pia 
pass  over  into  the  sclera,  but  the  arachnoid,  as  such,  is  lost  before 
this  occurs;  as  a  result,  the  two  lymph  spaces  between  these  three 
layers  become  one.  The  nerve  fibers  penetrate  the  sclera  through 
the  lamina  cribrosa.  As  they  pass  through  this  coat,  they  lose  the 
myelin  sheath,  so  that  they  become  amyelinated  fibers  when  they 
connect  with  the  retina. 

VITREOUS  BODY  AND  LENS 

Of  the  refractive  media  of  the  eyeball,  the  vitreous  and  aqueous 
humors  and  the  lens  are  yet  to  be  described. 

The  vitreous  humor,  or  body,  occupies  the  optic  cup,  or  vitreous 
chamber.  Upon  its  anterior  surface  is  a  deep  depression  in  which 
the  posterior  surface  of  the  lens  rests.  This  is  the  patellar  fossa. 
This  body  consists  of  a  fine  limiting  membrane,  the  hyaloid  membrane, 
a  delicate  homogeneous  structure  enclosing  the  substance  of  organ, 
which  is  composed  of  about  98  per  cent,  water  and  2  per  cent,  solid 
elements.  The  latter  comprise  connective  tissue  and  wandering 
cells,  and  some  fibrils.  The  vitreous  body  is  jelly-like  in  con- 
sistency. 

This  structure  is  traversed  by  a  small  canal,  called  the  canal 
of  Stilling,  or  hyaloid  canal.  This  extends  from  the  optic  nerve  to 
the  lens,  and  in  intrauterine  life  is  occupied  by  a  branch  of  the  reti- 
nal artery,  the  hyaloid  artery,  that  passes  to  the  lens. 

The  aqueous  humor  is  practically  lymph.  It  occupies  the  an- 
terior and  posterior  chambers,  and  as  a  refractive  medium  is 
unimportant. 

The  crystalline  lens  is  the  most  important  refractive  medium 
of  the  eyeball.  It  is  a  solid,  biconvex  body  measuring  about  9  to 
10  mm.  in  its  transverse  dimension  and  from  3.5  to  4  mm.  antero- 
posterior^. The  latter  dimension  varies  with  the  amount  of 
accommodation.  In  the  adult  it  weighs  about  180  milligrams  and 
at  birth  about   120  milligrams.     The  curvature  of  the  posterior 


5i6 


PRACTICAL   HISTOLOGY 


surface  is  the  greater  but  is  practically  fixed.  The  anterior  curvature 
is  chiefly  the  one  that  changes  in  accommodation. 

The  lens  consists  of  a  cap  side  within  which  is  the' lens  substance. 
The  capsule  is  a  transparent  and  apparently  homogeneous  membrane 
that  is  about  twice  as  thick  upon  the  anterior  surface  as  upon  the 
posterior.  The  posterior  surface  is  in  contact  with  the  hyaloid 
membrane  of  the  vitreous  humor  while  the  anterior  surface  touches 
the  posterior  surface  of  the  iris.  To  the  capsule  the  fibers  of  the 
suspensory  ligament  are  fastened. 

The  lens  substance  consists  of  the  lens  cells  and  lens  fibers.  The 
cells  are  columnar  in  the  early  childhood  and  gradually  reduce  in 


Fig.  285. — Capsule  and  Epithelium  of  a  Lens  of  Adult  Man. 

(Lewis  and  Stohr.) 

C,   Tangential  section.     D,    Meridional  section  across  the  equator  of  the  lens: 

1,  capsule;   2,   epithelium;  3,  lens  fibers.       X  240. 


height  as  age  advances  so  that  in  the  elderly  individuals  they  may 
be  flattened  elements.  These  cells  are  few  in  number  and  are  found 
only  on  the  anterior  surface  of  the  lens  substance,  just  beneath  the 
capsule ;  here  they  form  a  single  layer  of  cells.  Toward  the  equator  of 
the  lens  these  cells  successively  lengthen  so  that  at  the  equator 
they  are  lens  fibers. 

The  lens  fibers  are  simply  the  elongated  and  modified  lens  cells. 
This  change  is  permanent  and  the  fibers  cannot  reproduce  themselves. 
As  the  fibers  become  older  the  nucleus  is  gradually  lost  and  the 


THE   EYEBALL  AND   LACRIMAL  SYSTEM  517 

substance  of  the  fiber  seems  to  lessen  and  become  hardened,  forming 
dense  tough  structures.  The  nuclei  are  said  to  be  left  at  the  equa- 
torial region  of  the  lens  where  they  form  the  nuclear  zone. 

The  suspensory  ligament  of  the  lens  is  really  a  continuation  of  the 
hyaloid  membrane  reinforced  by  a  large  number  of  fibers  that  pass 
from  the  anterior  and  posterior  layers  of  the  capsule.  The  fibers 
from  the  anterior  layer  converge  in  groups  and  are  attached  to  de- 
pressions between  the  ciliary  processes;  those  from  the  posterior 
layer  have  a  similar  course  and  are  attached  to  the  summits  of  the 
processes.  The  two  layers  of  the  ligament  form  a  wedge-shaped 
area  around  the  equator  of  the  lens  and  this  is  known  as  the  canal  of 
Petit.  This  is  a  lymph  channel  and  the  anterior  layer  of  the  liga- 
ment is  not  complete,  permitting  communication  between  this 
space  and  the  posterior  chamber  of  the  eyeball.  The  region  between 
the  ciliary  processes  and  the  margin  of  the  lens  is  known  as  the  zone 
of  Zinn  {zonula  ciliaris) . 

The  chambers  of  the  eyeball  are  anterior,  posterior  and  vitreous 
or  optic  cup.  The  anterior  lies  between  the  iris  and  cornea,  the 
posterior  between  the  iris  and  capsule  and  suspensory  ligament  of 
the  lens,  and  the  vitreous  is  occupied  by  the  vitreous  body.  These 
are  large  lymph  spaces,  and  are  connected  with  one  another,  and 
with  the  other  spaces  of  the  eyeball. 

The  circulation  of  the  eyeball  is  carried  on  by  the  central  artery 
of  the  retina,  the  long  and  short  posterior  and  the  anterior  ciliary 
arteries. 

The  retinal  artery  passes  into  the  eyeball  through  the  center  of 
the  optic  nerve,  and  forms  a  whorl  of  branches  upon  its  entrance. 
These  vessels  extend  to  the  ora  serrata.  The  layer  of  rods  and  cones 
and  the  macula  lutea  possess  no  blood-vessels.  The  arterioles 
are  terminal  and  do  not  anastomose  with  one  another.  The  blood 
is  collected  by  venous  stems,  which  form  the  central  vein  of  the  retina 
that  has  a  course  parallel  to  the  artery. 

The  short  posterior  ciliary  arteries  are  about  twenty  in  number. 
They  pierce  the  sclera  near  the  exit  of  the  optic  nerve  in  a  circle 
called  the  circle  of  Zinn  and  pass  into  the  choroid.  As  they  pass 
through  the  sclera,  they  give  off  branches  that  supply  the  posterior 
half  of  this  coat.     In  the  choroid,  these  vessels  form  the  layer  of 


5i8 


Cornea. 


PRACTICAL  HISTOLOGY 
S    >)>]'$       ff'      1 


a  Anterior  ciliary  artery. 

a'  Anterior  ciliary  vein. 

0  Connection  with  circulus  iridicus  major 

y  Connection  with  choriocapillaris. 

5  Arterial  episcleral  branches. 

5'  Venous  episcleral  branches. 

e  Arterial  conjunctival  branches. 

e'  Venous  conjunctival  branches. 

t;  Arterial  branches  to  corneal  junction. 

77'  Venous  branches  to  corneal  junction. 

V  Venae  vorticosae. 

S  Venous  sinus  of  sclera. 


Fig.  286. — Vessels  of  the  Eye. 

External  tunic,  stippled;  middle  tunic,  white;  internal  tunic  and  optic  nerve, 

stippled  criss-cross;    arteries,  light;  veins,  dark. 
Central  vessels  of  retina;  a,  artery;  a',  vein;  b,  c,  d,  anastomoses  with  vessels 

of  sheath,  short  posterior  ciliary  arteries  and  choroidal  vessels,  respectively. 
A,  inner,  B,  outer  sheath  vessels;  1,  short  posterior  ciliary  artery;  /',  vein;  II, 

episcleral    artery;    //',   veins;  III,  capillaries  of  choriocapillar i       1,   long 

posterior  ciliary  artery;   2.  circulus  iridicus  major;  3,  branches^to  ciliary 

body;  4,  to  iris,    (Stohr's  Histology.} 


THE    EYEBALL   AND    LACRIMAL   SYSTEM  519 

large  vessels  and  the  choriocapillaris.  Their  branches  anastomose 
with  branches  of  all  others,  including  those  of  the  central  artery  of 
the  retina. 

The  long  posterior  ciliary  arteries  pierce  the  sclera  near  the  optic 
nerve,  and  pass  to  the  ciliary  region  between  the  choroid  and  sclera. 
At  the  base  of  the  iris,  they  form  a  circle  of  vessels,  the  circulus 
arteriosus  iridicus  major,  which  sends  branches  to  the  ciliary  proc- 
esses, the  choroid  and  the  iris;  the  latter  branches  pass  to  the  pupillary 
region,  where  they  form  the  circulus  iridicus  minor. 

The  anterior  ciliary  arteries  are  derived  from  the  vessels  of  the 
recti  muscles.  These  penetrate  the  sclera  near  the  corneoscleral 
junction  about  2  mm.  from  the  margin  of  the  cornea.  Their  branches 
nourish  the  anterior  half  of  the  sclera,  the  conjunctiva,  the  ciliary 
muscle,  and  the  anterior  half  of  the  choroid;  they  connect  with  the 
circulus  iridicus  major,  and  form  a  network  of  capillaries  at  the 
corneoscleral  junction.  Around  the  optic  nerve,  there  is  some 
anastomosis  between  the  branches  of  the  ciliary  arteries. 

Most  of  the  blood  is  returned  by  the  venae  vorticosae,  which  are 
four  to  six  in  number.  These  run  a  course  entirely  different  from  that 
of  the  arteries.  Each  is  formed  by  a  whorl  of  veins,  and  passes  through 
the  sclera  to  empty  into  the  ophthalmic  veins.  The  blood  from  the 
anterior  ciliary  arteries  is  carried  by  the  anterior  ciliary  veins  that 
run  parallel  to  the  arteries.  These  also  receive  the  blood  from  the 
episcleral  spaces. 

The  lymphatics  are  extensive,  and  form  a  series  of  intercommuni- 
cating spaces. 

Anteriorly,  the  spaces  in  the  cornea  communicate  with  those  of 
the  sclera,  and  with  the  canal  of  Schlemm  and  the  anterior  chamber, 
by  means  of  the  spaces  of  Fontana. 

The  anterior  chamber  communicates  with  the  posterior  chamber, 
and  through  this,  with  the  canal  of  Petit. 

Posteriorly,  the  lymphatics  of  the  optic  nerve  communicate  with 
the  subarachnoidean  space,  on  the  one  hand,  and  the  hyaloid  canal 
and  perivascular  spaces  of  the  retina,  on  the  other. 

The  space  of  Tenon  lies  external  to  the  sclera,  and  receives  lymph 
from  the  subscleral  space,  directly,  and  by  way  of  the  channels 
around  the  venae  vorticosae;  the  lymph  is  sent  to  the  spaces  around 


520  PRACTICAL   HISTOLOGY 

the  optic  nerve.  The  latter  communicate  with  those  of  the  central 
nerve  system. 

Some  describe  the  lymphatic  spaces  under  two  sets,  anterior  and 
posterior.  The  anterior  include  the  canal  of  Petit,  the  lymph  spaces 
of  the  ciliary  region  and  iris,  the  spaces  of  Fontana,  anterior  and 
posterior  chambers  and  the  corneal  spaces.  The  posterior  set  in- 
cludes the  spaces  of  the  vitreous  humor,  retina  the  subscleral,  or 
suprachoroidal  spaces,  the  perivascular  spaces  of  retina  and  choroid, 
the  capsule  of  Tenon  and  the  subarachnoid  and  subdural  spaces  of  the 
brain  continued  along  the  optic  nerve  to  the  eyeball.  These  com- 
municate freely  with  each  bther  through  the  zonule  of  Zinn  region 
and  through  the  lymph  channels  around  the  vessels. 

The  nerves,  long  and  short  ciliary,  supply  the  choroid  and  pass 
between  it  and  the  sclera;  at  the  ciliary  body,  they  form  the  ciliary 
ganglion  plexus,  that  supplies  the  ciliary  muscle,  iris  and  cornea 
and  vessels.  Those  of  the  iris  form  a  circular  plexus.  The  nerves 
of  the  cornea  have  been  considered. 

THE  APPENDAGES  OF  THE  EYEBALL 

The  appendages  are  the  eyelids,  conjunctiva  and  the  caruncle. 
The  eyelid  consists  of  a  double  fold  of  skin,  the  under  surface 
of  which  has  become  modified  to  form  a  mucous  membrane.  This 
is  the  conjunctiva,  which  is  composed  of  stratified  columnar  cells 
that  rest  upon  a  basement  membrane  and  tunica  propria.  These 
cells  are  four  or  five  layers  in  number  and  the  basal  elements  are  the 
smallest.  The  surface  cells  are  somewhat  pyramidal  in  form  with 
the  bases  forming  the  surface  and  the  apices  buried  among  the  other 
cells.  These  cells  seem  to  be  distensible.  Among  the  epithelial 
cells  some  goblet  cells  are  seen.  The  tunica  propria  is  thin  and 
firmly  attached  to  the  eyelid.  Over  its  greater  extent,  the  conjunc- 
tiva is  smooth,  but  toward  the  region  opposite  to  the  free  edge,  folds 
are  formed.  There  may  be  some  small  tubuloalveolar  glands  in 
the  tunica  propria  here.     They  are  the  glands  of  Waldeyer. 

Beneath  the  tunica  propria  is  found  a  dense  plate  of  white  fibrous 
tissue  called  the  tarsal  plate  {incorrectly  called  cartilage).  This  is 
wedge-shaped,  with  its  thicker  edge  at  the  margin  of  the  lid.     It 


THE   EYEBALL   AND    LACRIMAL   SYSTEM 


521 


extends  a  little  over  one-half  the  height  of  the  lid,  and  at  its  end 
an  accessory  tear  gland  is  found,  the  gland  of  Krause.  It  contains 
a  number  of  compound  racemose  glands,  the  ducts  of  which  open 


McR  *  Eli 

Fig.  287. — Sagittal  Section  of  Eyelid  of  a  Child  Six  Months  Old. 

(Stohr's  Histology.) 
1.  Skin:  E,   Epidermis;  C,   derma;  Sc,  subcutaneous  tissue;  Hb,  lanugo  hairs; 
K,   sweat-glands;    W,   eyelash;  Eh,   developing  lash;   W,   W",   portions  of 
follicle  of  eyelashes;   M,   portion  of  a  ciliary  gland.     2,   Orbicularis  pal- 
pebrarum   muscle:    O,    transverse   section   of   same;    McR,    tarsal   muscle. 

3,  tendon   of  levator  palpebrarum  superior;   mps,  superior  levator  muscle; 

4,  conjunctival  portion;  e,  epithelium;  tp,  tunica  propria;  at,  accessory 
tear  gland;  /,  tarsus;  m,  tarsal  gland  (Meibomian);  a,  arcus  tarseus  ex- 
ternus;  5,  margin  of  eyelid. 

upon  the  free  margin.     These  are  the  Meibomian,  or  tarsal  glands, 
and  number  about  thirty  in  the  upper,  and  about  twenty  in  the 


522 


PRACTICAL  HISTOLOGY 


lower  lid.     Thev 


Fig.  288. — Meibo- 
mian or  Tarsal 
Gland,  Recon- 
structed AFTER 
Born's  Wax-plate 
Method.  X  20. 
(Bohtn,  Davidoff 
and  Huber). 


resemble  sebaceous  glands  in  structure  and  the 
alveoli  are  filled  with  cells  that  are  in  varying 
stages  of  fatty  change;  the  ducts  are  lined  by 
stratified  squamous  cells.  At  the  margin  of  the 
lid  muscles  fibers  marginal  muscles  are  seen 
behind  the  ducts.  These  glands  secrete  an  oily 
substance  that  lubricates  the  edges  of  the  lids, 
prevents  them  from  uniting,  and  ordinarily 
keeps  the  tears  from  overflowing. 

Between  the  tarsal  plate  and  the  skin  surface, 
is  found  the  subcutaneous  fibrous  tissue.  In 
this  layer  is  the  muscle  of  the  eyelid,  which  is 
chiefly  of  the  voluntary  variety,  although  some 
smooth  muscle  is  present.  This  smooth  muscle 
tissue  constitutes  the  Superior  and  Inferior 
tarsal  muscles.  Some  voluntary  muscle  fibers 
are  found  between  the  cilia  and  Meibomian 
gland;  these  constitute  the  musculus  ciliaris 
Riolani.  In  the  tarsal  connective  tissue  are 
found  smooth  muscle  fibers  that  are  attached 
to  the  proximal  end  of  the  tarsal  plates;  these 
constitute  the  lid-muscle  of  Miiller.  Diffuse 
lymphoid  tissue  and  even  solitary  nodules  may 
be  seen  in  varying  quantities  in  the  tunica 
propria. 

The  skin  covers  the  outer  surface.  Its  struc- 
ture is  the  same  as  in  other  places,  and  it  con- 
tains many  sebaceous  and  sweat-glands  and  fine 
hairs.  Pigmented  cells  are  found  in  the  corium. 
Very  little  fat  is  found  in  the  loose  subcutane- 
ous tissue. 

At  the  edge  of  the  lid,  are  seen  two  rows  of 
heavy  hairs,  the  cilia,  or  eyelashes.  They  pass 
deeply  into  the  corium,  and  last  about  four 
months.  Between  the  cilia  and  the  ducts  of 
the  Meibomian  glands,  are  some  coiled  tubular 
structures  called  the  glands  of  Moll.     These  are 


THE   EYEBALL  AND   LACRIMAL   SYSTEM  523 

crrnininous  glands,  and  resemble  those  of  the  external  ear.     Their 
ducts  at  times  are  seen  to  open  into  the  follicles  of  the  cilia. 

The  skin  at  the  conjunctival  margin  forms  an  acute  angle,  while 
above  the  ciliary  region  the  angle  is  obtuse.  This  serves  to  dis- 
tinguish these  two  margins. 

The  conjunctiva  lines  the  internal  surfaces  of  the  eyelids,  and  is 
then  reflected  over  the  eyeball  from  the  insertion  of  the  muscles  to 
the  cornea.  It  is  loosely  attached  to  the  eyeball.  Here  the  strati- 
fied cells  alone  continue  upon  this  organ.  It  consists  of  peculiar 
stratified  columnar  cells,  basement  membrane  and  tunica  propria.  In 
the  latter  lymphoid  tissue  is  often  present  in  abundance.  That 
part  of  the  conjunctiva  which  is  reflected  from  the  eyelids  to  the 
eyeball  is  called  the  fornix  conjunctivae.  Here  the  conjunctiva  is 
loose,  attached  to  the  underlying  tissues  as  well  as  to  the  eyeball. 
This  laxity  and  the  presence  of  the  orbital  fat  permit  the  great 
freedom  of  motion  of  the  eyeball. 

At  the  inner  angle,  or  canthus,  of  the  lids  is  seen,  in  lower  animals, 
a  third  eyelid.  This  is  called  the  plica  semilunaris,  or  membrana 
nictitans.  In  lower  forms,  a  distinct  tarsal  plate  is  present,  which  is 
seldom  present  in  man.  Here  it  is  usually  a  small  fold,  covered  by 
stratified  squamous  cells,  in  which  some  glands  may  be  found. 

The  caruncle  is  a  little  patch  of  skin  at  the  inner  canthus.  It 
contains  hair  follicles,  sweat-glands,  adipose  and  muscle  tissues 
within  its  corium,  and  is  covered  by  stratified  squamous  cells.  A 
little  voluntary  striated  and  some  smooth  muscle  tissues  are  present. 

Within  the  eyelid,  two  arterial  arches  are  formed,  one  at  the 
proximal  edge  of  the  tarsus,  the  external,  and  the  other  at  the  edge 
of  the  lid,  the  internal.  These  arches  are  produced  by  the  vessels 
coming  from  the  inner  and  outer  canthi.  The  smaller  branches  pass 
to  the  glands  and  conjunctiva  of  the  lid,  where  they  form  delicate 
plexuses. 

The  lymphatics  form-  a  close,  delicate  plexus  beneath  the  con- 
junctiva, and  a  loose  set  at  the  upper  margin  of  the  lid,  that  com- 
municate with  each  other.  The  branches  of  the  latter  possess 
valves. 

The  nerves  give  off  branches  to  the  muscles  and  skin,  and  then 
form  a  plexus  beneath  the  conjunctiva.     The  latter  supplies  the 


524  PRACTICAL  HISTOLOGY 

glands,  cilia  and  conjunctiva,  forming,  in  the  latter,  a  subepithelial 
plexus  and  sensor  organs,  such  as  conjunctival  corpuscles  and  bulbs. 

THE  LACRIMAL  APPARATUS 

The  lacrimal  apparatus  consists  of  the  lacrimal  gland,  the  can- 
aliculi,  the  lacrimal  sac  and  the  nasolacrimal  duct. 

The  lacrimal  gland  is  a  compound  tubular  organ  of  a  serous  charac- 
ter. Like  the  mammary  gland,  it  is  a  multiple  compound  gland,  as 
it  is  composed  of  six  or  seven  individual  glands  merely  bound  into 
one  mass.  Each  has  its  own  duct  that  opens  upon  the  conjunctival 
surface. 


■ 


b 

'ft 

Fig.  289. — From  a  Section  of  a  Human  Lacrimal  Gland.      X  420. 

(Lewis  and  Stohr.) 

A,  Gland  body:  a,  Tubule  cut  across;  a',  group  of  tubules  cut  obliquely;  s, 
intercalated  tubule;  s',  intercalated  tubule  in  cross  section;  b,  connective 
tissue.  B,  Cross-section  of  an  excretory  duct:  e,  Two-rowed  cylindrical 
epithelium;  b,   connective  tissue. 

Each  gland  is  covered  by  a  delicate  capsule  of  white  fibrous  tissue 
that  divides  it  into  lobes  and  lobules.  The  lobules  consist  of  the 
tubular  acini,  which  are  lined  by  simple  columnar,  or  cuboidal  cells. 
The  cytoplasm  of  these  is  granular,  and  the  nuclei  have  a  basal 
position.  The  cells  that  have  just  discharged  their  secretion  are 
small  and  the  cytoplasm  is  granular.  During  the  resting  stage  the 
cell  becomes  swollen  and  the  cytoplasm  is  usually  clear.  The 
nucleus  has  a  basal  position.  With  the  discharge  of  the  secretion 
the  cells  are  again  smaller  and  more  granular.  These  cells  rest  upon 
a  basement  membrane,  containing  basket  cells,  which  is  supported 


THE   EYEBALL   AND   LACRIMAL   SYSTEM  525 

by  interstitial  connective  tissue  of  a  fibroelastic  nature.  The  intra- 
lobular and  interlobular  ducts  are  lined  by  simple  columnar  cells; 
the  main  ducts  are  lined  with  stratified  columnar  cells. 

The  blood-vessels  are  numerous  and  form  close  capillary  plexuses 
around  the  tubules. 

The  nerves  form  a  subepithelial  plexus,  but  the  exact  mode  of 
ending  is  not  known. 

Each  canaliculus  has  a  lining  of  stratified  squamous  cells  that  rest 
upon  the  tunica  propria  and  fibro-elastic  layer.  Outside  of  the 
tunica  propria  is  seen  some  voluntary  striated  muscle,  chiefly  longi- 
tudinally arranged. 

The  opening  of  the  canaliculus  is  called  the  punclum,  and  at  this 
point  some  of  the  muscle  fibers  are  circularly  disposed,  forming  a 
sphincter  muscle. 

The  sac  and  duct  are  lined  by  stratified  columnar  cells.  In  the 
tunica  propria,  considerable  diffuse  lymphoid  tissue  is  found.  Occa- 
sionally, in  the  lower  end  of  the  duct,  ciliated  epithelial  cells  are 
present. 

Within  the  orbit,  the  eyeball  is  surrounded  by  a  serous  membrane 
called  the  capsule  of  Tenon.  The  space  enclosed  is  the  space  of 
Tenon,  or  the  episcleral  lymph  space.  This  space  aids  in  the  move- 
ment of  the  eyeball. 


CHAPTER  XIX 
THE  EAR 

The  ear  {orgonan  auditus)  is  made  up  of  three  parts,  the  external, 
middle  and  internal. 

The  external  ear  receives  the  sound  waves  and  conducts  them  to 
the  middle  ear.  The  vibrations  of  the  drum  are  carried  across  the 
middle  ear  and  conducted  into  the  internal  ear,  where  they  are 
translated  into  the  proper  nerve  impulses  and  conveyed  to  the 
temporal  lobe  of  the  cerebrum. 

The  external  ear  consists  of  the  pinna  and  a  short  canal,  the 
external  auditory  canal. 

The  pinna,  or  auricle  is  covered  upon  both  surfaces  by  skin  and  in 
the  center  is  a  mass  of  elastic  cartilage.  It  is  very  irregular  but  is 
adapted  to  catch  the  sound  waves.  The  skin  is  in  no  way  different 
from  that  of  the  general  body  surface  and  possesses  fine  hairs  and 
some  sweat  glands.  Connected  with  the  small  hairs  are  large  se- 
baceous glands.  The  irregular  mass  of  elastic  cartilage  occupies 
the  pinna  proper  and  does  not  extend  into  the  lobule.  The  latter 
is  the  lower,  soft  portion  and  this  is  very  vascular.  The  cartilage 
is  surrounded  by  a  perichondrium  to  which  the  derma  and  the  in- 
trinsic aural  muscles  are  attached.  The  firm  attachment  of  the 
derma  prevents  movements  of  the  cartilage.  The  matrix  consists 
of  chiefly  elastic  tissue  that  forms  a  network  in  which  are  groups  of 
large  cartilage  cells  imbedded  in  a  small  amount  of  hyalin  substance. 
The  elastic  tissue  is  less  prominent  in  the  child  than  in  the  adult. 
In  the  child  at  birth  this  reticulum  responds  readily  to  the  reticulum 
stain  and  not  to  the  elastica  stain.  Adipose  tissue  is  not  present 
in  the  pinna. 

The  external  auditory  canal  consists  of  outer  cartilaginous  and 
inner  bony  portions.  Both  portions  are  lined  by  skin  which  is  an 
extension  of  that  of  the  pinna.     This  consists  of  stratified  squamous 

526 


THE   EAR  527 

cells  that  rest  upon  a  basement  membrane  and  derma.  In  the  skin 
of  the  outer  part  there  are  numerous,  large,  stiff  hairs,  sebaceous 
glands  and  some  coiled  tubular  glands  that  secrete  the  ear  wax. 
These  ecru  mi  nous  glands  are  analogous  in  structure  to  the  sweat 
glands;  the  functionating  cells,  however,  contain  some  fine  brown- 
ish pigment  granules.  The  derma  is  attached  to  the  tube-like  con- 
tinuation of  the  elastic  cartilage  of  the  pinna. 

The  skin  of  the  inner  part  is  thinner  and  is  attached  to  the  bony 
wall  of  the  canal.  Some  very  fine  hairs  may  be  present  in  the  outer 
part  but  near  the  tympanic  membrane  part  of  the  canal  hairs  and 
glands  are  absent.  The  uppermost  layers,  at  least,  of  the  external 
auditory  canal  move  constantly  from  within,  outward.  By  this 
means  the  cerumen  is  ordinarily  moved  to  the  outlet. 

THE  MIDDLE  EAR 

The  middle  ear  comprises  the  tympanum,  membrana  tympani, 
auditory  ossicles  and  auditory  tube. 

The  tympanum  {cavum  tympani)  consists  of  the  tympanic  cavity 
proper ',  the  attic  and  here  may  be  added  the  mastoid  cells.  The 
tympanic  cavity  proper,  or  atrium  is  a  narrow  space  that  is  nearly 
parallel  to  the  sagittal  plane  of  the  body.  It  measures  about  15 
mm.  in  height  and  length,  but  the  distance  between  the  lateral  and 
medial  walls  varies;  at  the  top  it  is  6  mm.,  in  the  middle  2  mm., 
at  the  bottom  4  mm.  About  the  level  of  the  tympanic  membrane 
the  tympanic  cavity  forms  a  recess  called  the  attic,  or  epitympanum. 
This  contains  most  of  the  incus  and  half  of  the  handle  of  the  malleus 
and  communicates  with  the  mastoid  antrum.  From  the  lower  part 
of  the  anterior  wall  the  auditory  tube  extends  to  the  pharynx. 
Upon  the  medial  wall  are  two  openings,  in  dried  specimens.  The 
upper  is  oval  in  shape  and  is  called  the  fenestra  vestibuli.  This 
measures  about  3  mm.  horizontally  and  1.5  mm.  vertically.  In  the 
fresh  condition  this  opening  is  blocked  by  the  foot  of  the  stapes  and 
its  annular  ligament.  Beneath  this  is  the  second  opening  that  is 
circular  in  outline.  This  is  the  fenestra  cochleae  and  in  the  fresh 
condition  it  is  closed  by  the  membrana  tympani  secundaria. 

The  tympanic  antrum  is  about  8  mm.  by  10  mm.  and  connects 


528 


PRACTICAL  HISTOLOGY 


the  epitympanum  with  the  mastoid  cells.  The  mastoid  cells  vary 
in  number  and  size  and  may  extend  almost  to  the  tip  of  the  mastoid 
process.  They  are  usually  quite  numerous  in  the  adult  and  are  said 
not  to  be  developed  until  the  sixth  year. 

The  tympanic  cavity  and  its  extensions  are  lined  with  a  mucous 
membrane  that  is  continuous  with  that  of  the  pharynx  through  the 
auditory  tube.     The  cells  are  of  the  pseudostratified  ciliated  variety, 


Fig.  290. — Vertical  Section  through  the   External  Auditory  Canal  and 

Tympanum. 

A,  Epitympanic  recess;  B,  tympanum;  C,  fenestra  ovalis  closed  by  foot  of  the 
stapes;  Mem.,  tympanic  membrane.      (Radasch,  " Manual  of  Anatomy.") 


chiefly,  though  parts  of  the  cavity  may  possess  nonciliated  cells 
and  even  stratified  squamous  cells.  Upon  the  ossicles,  ligaments 
and  tympanic  membrane  the  cells  are  nonciliated.  These  cells  rest 
upon  a  delicate  basement  membrane  and  fibroelasiic  tunica  propria. 
The  latter  is  attached  to  the  periosteum  of  the  bony  boundaries 
very  firmly.  Small  mucous  glands  are  found  in  the  tunica  propria 
and  diffuse  lymphoid  tissue  may  also  be  present.     The  antrum  and 


THE   EAR  529 

mastoid  cells  are  lined  by  low  polygonal  or  flattened  epithelial  cells. 
The  tunica  propria  throughout  is  quite  vascular. 

The  tympanic  membrane  is  an  elliptical,  disc-like  membrane  that 
slopes  downward,  medially  and  backward.  It  is  about  10  mm.  in 
its  vertical  dimension  and  about  9  mm.  from  side  to  side.  It  sepa- 
rates the  middle  ear  from  the  external  auditory  canal.  Its  circum- 
ference is  thickened  by  the  circularly  directed  fibers  of  the  annulus 
fibrocartihigincus,  that  attaches  it  to  the  circumference  of  the  medial 
end  of  the  external  auditory  canal.  The  handle  of  the  malleus  is 
attached  to  its  medial  surface  and  above  this  attachment  and  promi- 
nence the  membrane  is  flaccid  (pars  flaccida).  The  bulk  of  the 
membrane  is  tense  (pars  tensa).  The  central  part  of  the  membrane 
is  drawn  slightly  inward  by  the  attached  handle  of  the  malleus  and 
this  part  of  the  membrane  is  called  the  umbo.  Externally,  it  is 
covered  by  stratified  squamous  cells  continued  from  the  skin.  In 
this  location,  the  stratum  corneum  is  nucleated,  and  the  corium  is 
thin,  except  in  the  region  of  the  handle  of  the  malleus.  The  middle 
portion  consists  of  white  fibrous  tissues  arranged  as  radial,  or  ex- 
ternal, and  circular ,  or  internal  fibers. 

The  former  becomes  thinner  toward  the  center  of  the  tympanum 
and  disappears  entirely.  The  circular  fibers  are  more  numerous 
externally,  and  become  thinner  toward  the  handle  of  the  malleus, 
where  they  disappear.  Between  these  two  layers  is  a  small  amount 
of  loose  connective  tissue.  Peripherally,  the  fibrous  layer  becomes 
thickened  to  form  the  annulus  fibrosus.  The  internal  surface  is 
covered  by  simple  squamous,  or  columnar  cells  that  rest  upon  a 
basement  membrane.  In  the  flaccid  area  of  the  drum,  the  middle 
layer  is  absent,  so  that  the  internal  and  external  layers  touch  each 
other. 

The  ear  bones  are  the  malleus,  incus  and  stapes.  These  are 
small  masses  of  osseous  tissue,  by  means  of  which  the  sound  waves 
are  transmitted  from  the  drum  to  the  internal  ear.  In  the  thickest 
portions  they  possess  Haversian  systems.  Their  articular  surfaces 
are  covered  with  hyalin  cartilage.  The  stapes  alone  possesses  a 
marrow  cavity. 

The  malleus  is  the  largest  having  a  length  of  8  to  9  mm.     The 

main  parts  are  the  head  and  handle.     By  means  of  the  former  it 
34 


530  PRACTICAL  HISTOLOGY 

articulates  with  the  incus  and  by  means  of  the  latter  it  is  attached 
to  the  tympanic  membrane.  The  incus  is  next  in  size  and  means 
of  the  body;  it  articulates  with  the  head  of  the  malleus  and  by  means 
of  the  long  process  it  articulates  with  the  stapes.  The  stapes  is  the 
smallest  and  most  delicate  of  the  ossicles.  Its  head  articulates  with 
the  long  process  of  the  incus  and  its  foot,  or  base  rests  in  the  fenestra 
vestibuli,  to  the  boundaries  of  which  it  is  attached  by  means  of  the 
annular  ligament. 

The  muscles  of  the  middle  ear  are  the  stapedius  and  tensor  tympani. 
The  stapedius  lies  entirely  within  the  tympanic  cavity  and  is  inserted 
into  the  neck  of  the  stapes.  By  the  contraction  of  this  muscle  the 
anterior  end  of  the  base  is  tilted  laterally  and  the  posterior  end  me- 
dially, compressing  the  lymph  within  the  vestibule.  It  is  the  smallest 
muscle  in  the  body.  The  tensor  tympani  muscle  comes  into  the  tym- 
panic cavity  through  a  special  canal  and  is  inserted  upon  the  medial 
edge  of  the  anterior  surface  of  the  handle  of  the  malleus  in  such  a 
manner  that  when  the  muscle  contracts  the  handle  is  drawn  medially 
and  the  membrane  is  made  tense. 

The  auditory  tube,  or  better  pharyngotym panic  tube,  extends 
from  the  lower  part  of  the  anterior  wall  of  the  tympanic  cavity  to  the 
pharynx.  It  is  about  36  mm.  in  length  and  is  directed  downward  at 
an  angle  of  about  300  to  400  to  the  horizontal  plane  and  forward 
and  medially  at  an  angle  of  about  450  to  the  sagittal  plane.  It  opens 
in  the  lateral  wall  of  the  nasopharynx. 

Theirs/  part,  about  12  mm.  is  called  the  bony  portion  as  the  tunica 
propria  is  attached  to  the  periosteum  of  the  bony  boundary.  The 
medial  two-thirds,  about  24  mm.  is  called  the  cartilaginous  portion 
because  outside  of  the  tunica  propris  there  is  a  f-shaped  mass 
of  elastic  cartilage.  At  the  pharyngeal  extremity  the  cartilage 
bulges  the  pharyngeal  mucosa  in  a  hook-like  manner  and  this 
peculiar  ridge  is  called  the  torus  tubarius. 

The  osseous  portion  of  the  auditory  tube  is  lined  by  a  thin  mucous 
membrane  that  is  closely  adherent  to  the  periosteum.  The  lining 
cells  are  pseud o-stratified  ciliated  elements.  Glands  are  absent.  In 
the  cartilaginous  portion,  the  mucosa  is  thicker,  and  is  lined  by 
stratified  ciliated  cells,  among  which  there  are  a  large  number  of 
goblet    cells.     In  the  tunica  propria,  mucous  glands  and  diffuse 


THE   EAR  531 

Lymphoid  tissue  are  seen,  and  the  latter  may  be  formed  into  solitary 
nodules    near    the    pharyngeal    end.     These    constitute    the    tubal 

tonsils. 

The  membrane  closing  the  fenestra  rotunda  that  leads  to  the 
internal  ear  (to  the  cochlear  duct)  consists  of  connective  tissue. 
Its  middle  ear  surface  is  covered  by  nonciliated  cells,  while  that  which 
lies  in  the  internal  ear  is  covered  by  endothelial  cells.  The  base  of 
the  stapes  with  the  annular  ligament  that  attaches  it  to  the  edge  of 
the  foramen,  completely  occludes  the  fenestra  ovalis,  that  leads  to 
the  vestibule. 

The  blood  supply  to  the  tympanic  membrane  is  important.  Its 
external  surface  is  supplied  by  capillaries  derived  from  the  vessels  of 
the  external  canal,  while  the  inner  surface  receives  vessels  from  those 
of  the  middle  ear.  The  mucosa  of  the  auditory  tube  receives  blood 
from  both  the  middle  ear  and  pharyngeal  vessels. 

Lymphatic  vessels  follow  those  of  the  circulatory  system.  Those 
of  the  external  surface  of  the  membrana  tympani  empty  into  those 
of  the  external  canal,  while  those  of  the  inner  surface  empty  into 
those  of  the  tympanum.  The  latter  lie  in  the  deeper  portions  of 
the  tunica  propria,  and  at  intervals  possess  dilatations. 

The  nerves  of  the  external  surface  of  the  tympanic  membrane  are 
derived  from  the  auriculotemporal  and  the  auricular  branches  of  the 
vagus.  Both  form  a  close  plexus.  This  supplies  the  external 
surface  by  a  subepithelial  plexus.  The  inner  surface  is  supplied  by 
the  tympanic  plexus,  wThich  sends  branches  to  the  epithelial  layer. 
Occasionally,  minute  ganglia  are  present.  The  auditory  tube  re- 
ceives fibers  from  the  tympanic,  as  well  as  from  the  pharyngeal 
plexuses. 

THE  INTERNAL  EAR 

The  internal  ear,  or  labyrinth,  consists  of  two  main  divisions,  the 
osseous  labyrinth  and  the  membranous  labyrinth.  The  osseous 
labyrinth  comprises  the  vestibule,  semicircular  canals  and  the  coch- 
lea. The  membranous  labyrinth  consists  of  the  sacculus,  utricu- 
lus,  semicircular  canals  and  the  cochlear  duct. 

The  labyrinth  consists  of  the  osseous  and  membranous  portions, 
which  are  separated  from  each  other  by  a  lymph  space.     The 


532 


PRACTICAL  HISTOLOGY 


bony  labyrinth  surrounds  the  membranous  portion,  and  is  separated 
from  it  by  the  perilymph.  Within  the  membranous  part  is  the 
endolymph. 

SACCULUS  AND  UTRICULUS 

The  vestibule  lies  between  the  semicircular  canals  behind,  and 
the  cochea,  in  front.  It  is  about  6  mm.  anteroposteriorly,  from  4  to  5 
mm.  from  above  downward  and  3  mm.  from  without  inward.  Upon 
its  lateral  wall  is  seen  the  fenestra  vestibuli  that  is  closed  by  the  base 
of  the  stapes  and  its  ligament.  It  lodges  the  membranous  sacculus 
and  utriculus. 


Fig.  291. — Isolated  Membranous  Labyrinth  of  the  Right  Side. 
A,   Ductus  endolymphaticus.      (Radasch,  " Manual  of  Anatomy.") 

The  bony  walls  of  the  vestibule  are  covered  by  periosteum,  which 
is  lined  by  a  layer  of  endothelial  cells  continued  over  the  trabecular, 
that  extend  from  the  periosteum  to  the  membranous  labyrinth. 
From  this  point  the  endothelium  continues  over  the  external 
surface  of  the  membranous  labyrinth. 

The  sacculus  and  utriculus  are  two  membranous  sacs  of  unequal 
size,  that  occupy  the  vestibule  and  do  not  communicate  with  each 
other  directly,  but  with  the  ductus  endolmyphaticus  by  two  small 
canals.     The  sacculus  is  the  smaller,  and  lies  anterior  to  and  below 


THE   EAR  533 

the  utriculus.  It  measures  about  2  by  3  mm.  and  is  ovoid  in  form. 
The  utriculus  is  connected  with  the  ampullae  of  the  superior  and 
lateral  semicircular  canals,  while  the  sacculus  communicates  with 
the  cochlear  duct  of  the  membranous  labyrinth  by  means  of  the 
ductus  reuniens. 

The  walls  of  the  membranous  saccule  and  utricle  are  composed  of 
bundles  of  white  fibrous  tissue  arranged  into  two  layers  of  variable 
thickness,  5  to  15  microns.  The  thickest  portions  are  where  the 
lKTve  fibers  leave  the  maculae  acusticae  and  maculae  cribrosae.  The 
cells  lining  these  vesicles  consist  of  simple  polygonal  epithelium,  3  to 
4  microns  in  height,  except  over  f  he  maculae  acusticae,  where  they  are 
of  the  neuro-epithelial  variety.  Upon  approaching  these  areas,  the 
polygonal  change  to  caboidal  and  become  progressively  higher  until 
a  height  of  30  microns  is  reached.  These  cells  are  of  two  varieties, 
sustentacula!*,  or  supportive,  and  special,  neuro-epithelial,  or  hair- 
cells. 

The  sustentacular  cells  are  very  long,  irregular  columns,  the 
basal  portions  of  which  are  branched.  The  large  nuclei,  located  at 
various  levels  in  the  inner  half  of  the  cell,  produce  a  bulging  of  the 
cell-body.  The  granular  cytoplasm  possesses  pigment  granules  of  a 
yellowish  color. 

The  special,  or  hair-cells,  are  also  columnar,  but  not  as  long  as 
the  preceding,  and  extend  through  only  one-half  of  that  layer.  The 
basal  portion  of  these  cells  is  broad,  and  contains  large  round  nucleus; 
the  basal  part  is  continued  between  the  sustentacular  cells  toward  the 
basement  membrane  for  a  variable  distance  and  usually  ends  in  a 
small  knob.  In  the  epithelial  layer  the  terminal  fibrils  of  the 
vestibular  nerve  form  a  plexus  and  the  fibrils  of  this  plexus  terminate 
around  these  extensions  of  the  hair  cells.  The  distal  end  is  rounded 
and  possesses  a  cuticular  border,  the  cupola,  from  which  projects  a 
conical  cilium  20  microns  long.  This  extends  into  the  endolymph. 
Closer  examination  shows  that  the  cilium  consists  of  many  fine 
hairs.  The  cytoplasm  of  these  cells  is  granular  and  contains  a 
yellowish  pigment. 

The  otoliths,  or  otoconia  are  small,  prismatic  calcium  carbonate 
crystals,  1  to  15  microns  long,  occuring  in  the  vesicles,  and  imbedded 
in  a  gelatinous  substance,   the  otolith  membrane,  that  covers  the 


534  PRACTICAL  HISTOLOGY 

neuroepithelial  cells.  This  otolith  membrane  contains  many  of 
these  prisms. 

The  ductus  endolymphaticus  and  its  dilated  extremity,  the 
sacculus,  have  the  same  structure  as  saccule  and  utricle. 

A  plexus  of  nerve  fibers  is  found  beneath  the  neuro-epithelium.  The 
fibers  extend  into  the  epithelial  layer,  and  as  they  pierce  the  base- 
ment membrane,  the  myelin  sheath  blends  therewith,  and  leaves 
the  dendrite  free.  These  latter  form  fibrillae  that  are  terminate  in 
relation  with  the  neuro-epithelial  (hair)  cells;  some  pass  higher 
between  the  supportive  cells. 

In  these  areas,  the  capillary  plexuses  are  especially  numerous. 

THE  SEMICIRCULAR  CANALS 

The  osseous  semicircular  canals  are  behind  and  above  the 
vestibule.  They  are  three  in  number  and  are  called  superior, 
lateral  and  posterior.  Each  forms  about  two-thirds  of  a  circle  and 
is  about  i.o  to  1.5  mm.  in  diameter.  One  extremity  of  each  is 
dilated  and  this  dilation  is  an  ampulla  that  is  about  2  mm.  in  diameter. 
These  canals  communicate  with  the  vestibule  by  five  openings. 
The  superior  canal  is  vertical  and  is  placed  transversely  to  the  long 
axis  of  the  petrous  portion  of  the  temporal  bone.  Its  length  is 
about  18  mm.  The  lateral  canal  is  placed  almost  horizontally  and 
measures  12  to  15  mm.  in  length.  The  posterior  canal  is  20  mm.  in 
length.  The  opposite  lateral  canals  lie  in  the  same  plane  while  the 
superior  canal  of  one  ear  is  parallel  to  the  posterior  canal  of  the  other 
ear. 

The  membranous  semicircular  canals  are  united  to  the  periosteum 
by  trabecule,  as  in  the  preceding,  and  the  endothelial  cells  pursue 
the  same  course  in  the  lymph  space.  The  epithelium  resembles 
that  of  the  saccule  and  utricle,  being  polygonal,  but  slightly  larger, 
varying  from  12  to  16  microns.  Specialized  areas,  cristas  acusticae, 
are  found  in  the  floor  of  the  ampullae  (dilated  portion  at  the  end  of 
each  canal).  Here  the  thickened  fibrous  wall  forms  the  transverse 
septum.  The  specialized  areas  resemble  those  of  the  saccule  and 
utricle.  The  hairs  of  the  neuro-epithelial  cells  are  unusually  long, 
some  reaching  to  the  middle  of  the  lumen.  They  are  called  the 
auditory  hairs,  and  arise  from  the  cupola  of  the  cells. 


THE  EAR  535 

The  nerve  fibers  pass  to  the  thick  transverse  septum,  and  form  a 
plexus  from  which  finer  fibers  follow  the  same  course  as  in  the 
saccule  and  utricle. 

The  blood-vessels  are  distributed  in  the  same  manner. 

THE  COCHLEA 

The  cochlea  represents  a  tapering  tube  of  20  to  30  mm.  length 
spirally  wound  for  about  two  and  three-quarters  turns  about  a 
vertical  bony  axis,  the  modiolus.  The  broad  portion  is  the  base 
that  measures  about  9  mm.  across  and  is  in  relation  with  the  inferior 
fossula  of  the  internal  auditory  meatus.  The  end  of  the  coil  is 
the  apex,  or  cupola;  it  is  about  5  mm.  above  the  base  and  2  mm. 
above  the  modiolus.  The  basal  end  of  the  tube  is  2  mm.  in  diameter. 
The  modiolus,  or  axis  is  a  conical  mass  about  3  mm.  high  and  is 
pierced  by  many  foramina  for  the  transmission  of  nerve  fibers. 
Upon  the  tube  side  the  modiolus  sends  out  a  bony  shelf  that  extends 
about  halfway  across  the  tube  and  is  called  the  lamina  spiralis 
(ossea).  The  division  of  the  tube  is  completed  by  the  basilar  mem- 
brane that  extends  from  the  spiral  lamina  to  the  lateral  wall  of  the 
osseous  tube.  As  a  result  of  these  shelves  two  passageways  are 
formed,  the  upper  the  scala  vestibuli  and  the  lower  the  scala  tympani. 
At  the  modiolus  edge  of  the  spiral  lamina  there  is  a  canal  that 
extends  the  length  of  the  spiral  shelf  and  in  this  spiral  canal  the 
ganglion  of  Corti  {ganglion  s  pirate)  is  lodged.  The  spiral  lamina 
and  the  basilar  membrane  extend  to  within  a  short  distance  of  the 
end  of  the  cochlear  tube  and  at  this  point  the  two  scala  communicate 
with  each  other.  This  communication  is  called  the  helicotrema. 
Both  contain  perilymph. 

The  ductus  cochlearis,  or  scala  media,  is  a  delicate,  triangular, 
membranous  canal  that  lies  in  the  scala  vestibuli;  its  outer  basal 
angle  is  attached,  externally,  to  the  outer  wall,  and  the  inner  angle, 
internally,  to  the  lamina  spiralis.  It  contains  the  endolymph,  and 
has  an  important  epithelial  lining.  The  basilar  membrane  separates 
it  from  the  scala  tympani,  and  the  membrane  of  Reissner  from  the 
scala  vestibuli.  The  /a/ter^membrane  is  quite  thin,  about  3  microns, 
and  extends  from  the  lamina  spiralis  (internal  to  the  crista)  to  the 


536 


PRACTICAL   HISTOLOGY 


bony  wall  of  the  scala  vestibuli  at  an  angle  of  about  450.  Upon  its 
vestibular  wall,  it  is  covered  by  a  layer  of  pigmented  endothelial  cells 
which  rest  upon  the  middle  connective  tissue  layer,  in  which  cap- 
illaries are  found.  The  epithelial  lining  of  its  inner  surface  consists 
of  a  single  layer  of  polygonal  cells.  The  outer  wall  of  the  scala 
media,  for  about  two-thirds  of  its  distance  from  the  upper  angle,  is 
covered  by  cuboid al  cells,  within  which  there  are  quite  a  number  of 
capillaries,  a  very  unusual  condition.     This  is  the  stria  vascularis. 


Modiolus. 
\ 


Scala  vestibuli. 


Ganglion    — "~  ~/ 
spirale.  / 


-,     /   ""  Scala  tympani. 


Ganglion 
vestibulare 


•*  ^.  Ramus 
cocblearis. 


Ramus 
vestibularis.    , 


of  the  nervus 
acusticus. 


Meatus  acusticus  internus. 

Fig.  292. — Horizontal  Section  of  the  Cochlea  of  a  Kitten.    X  8. 

(Stohr's  Histology.) 

The  winding  ductus  cochlearis,  x,  crossed  the  plane  of  section  five  times.     Above 
it  in  every  case  is  the  scala  vestibuli,  and  below  it  is  the  scala  tympani. 

At  the  lower  margin  of  the  latter  is  a  small  projection,  the  promi- 
nentia spiralis ;  this,  with  the  lower  part  of  the  outer  wall,  is  covered 
by  flattened  cells  that  become  columnar  as  the  basilar  membrane 
is  reached.  The  tissue  external  to  these  cells  is  quite  thick,  and 
extends  over  the  vestibular  wall  above  the  attachment  of  Reissner's 
membrane,  and  below  the  attachment  of  the  basilar  membrane. 
This  is  the  ligamentum  spirale.  At  the  attachment  of  the  basilar 
membrane  this  ligament  forms  a  projection  called  the  crista  basilaris. 
The  floor  of  the  ductus  cochlearis  (tympanic  side)  consists  of 
the  basilar  membrane  that  unites  the  spiral  prominence  to  the 


THE    EAR 


537 


spiral  lamina;  this  is  completed  by  the  limbus  that  extends  from  the 
end  of  the  spiral  lamina  to  the  attachment  of  Reissner's  membrane. 
The  outer  portion  of  the  limbus  is  thicker  near  the  membrane, 
due  to  an  increase  in  the  periosteum.  This  portion  contains  clefts 
and  depressions  that  deepen  toward  the  inner  half,  at  which  point 


Nerve. 


Inner 


Outer 


Membrana  Tympanal 
Nuel's    Deiter's   basilaris.    lamella, 
space.        cells. 


Pillar  cells. 


Fig.  293. — Diagram  of  the  Structure  of  the  Basal  Wall  of  the  Duct 
of  the  Cochlea.     (Stohr's  Histology.) 

A,  View  from  the  side.  B,  View  from  the  surface.  In  the  latter  the  free  surface 
is  in  focus.  It  is  evident  that  the  epithelium  of  the  sulcus  spiralis,  lying  in 
another  plane,  as  well  as  the  cells  of  Claudius,  can  be  seen  distinctly  only 
by  lowering  the  tube.  The  membrana  tectoria  is  not  drawn.  The  spiral 
nerves  are  indicated  by  dots. 


the  cleft  is  quite  deep,  and  little  projections,  separated  by  lateral 
clefts,  give  rise  to  the  auditory  teeth,  which  number  about  2500. 
These  teeth  and  projecting  areas  are  covered  by  simple  polygonal 
cells,  while  the  clefts  are  lined  by  columnar  elements.  The  inner 
half  of  the  limbus  consists  of  a  slightly  projecting  mass,  the  superior 


538  PRACTICAL   HISTOLOGY 

lip,  due  to  the  sudden  decrease  in  thickness,  and  a  lower  portion 
that  continues  over  the  bony  lamina  toward  the  basilar  membrane; 
the  latter  is  the  inferior  lip.  Between  these  lies  a  little  space,  the 
sulcus  spiralis,  due  to  the  sudden  decrease  in  thickness  of  the 
periosteum.     The  sulcus  is  lined  by  flat  cells. 

The  basilar  membrane  is  covered  on  its  tympanic  surface  by  the 
tympanic  lamella,  made  up  of  spindle-shaped  cells  and  delicate 
fibers,  representing  an  incomplete  change  to  endothelial  cells.  This 
is  continuous  with  the  periosteum  of  the  scala  tympani.  Above 
this  layer  is  the  membrana  propria,  that  represents  a  greatly  hyper- 
trophied  basement  membrane  and  seems  to  support  the  epithelium 
upon  its  upper  surface.  The  outer  end  of  the  basilar  membrane  is 
covered  by  the  cells  of  Claudius  that  continue  toward  the  outer 
wall  and  pass  into  columnar  and  flattened  elements  that  are  found 
upon  the  basilar  crest.  These  cells  possess  spherical  nuclei  imbedded 
in  a  slightly  granular  and  pigmented  cytoplasm;  they  represent  a 
continuation  of  the  cells  of  Hensen.  Between  the  limb  us  and  the 
cells  of  Claudius  lies  the  organ  of  Corti,  composed  of  neuro-epithe- 
lial  and  sustentacular  cells.  This  organ  is  divided  into  an  inner 
portion,  the  membrana  tectoria,  and  an  outer  part,  the  zona  pec- 
tinata. 

The  cells  of  the  organ  of  Corti  are  the  pillar,  hair  and  sustentacular 
cells. 

The  pillar  cells  are  peculiar  S-shaped  elements  possessing  a  striated 
body,  surrounded  by  a  narrow  band  of  cytoplasm.  The  latter  is 
thickened  at  the  base  {tunnel  side) ,  and  in  this  part  is  seen  the  nucleus. 
The  lower  end  rests  upon  the  basilar  membrane,  and  is  expanded  to 
form  the  foot;  the  upper  end  likewise  undergoes  an  expansion,  termed 
the  head.  These  cells  form  two  rows,  inner  and  outer;  they  articu- 
late above,  and  form  a  triangular  canal  called  Corti's  tunnel.  This 
contains  a  semi-solid  intercellular  substance.  The  inner  cell,  being 
shorter,  is  more  nearly  vertical,  and  its  head  bears  an  articular  facet 
for  the  reception  of  the  articular  head  of  the  outer  cell.  The  inner 
cells  are  more  numerous  and  thinner  than  the  outer,  about  6000  to 
4500,  respectively.  The  head  process  of  both  cells  continues  ex- 
ternally as  a  thin,  shelf-like  process  called  the  head-plate.  Of 
these,  the  inner  head-plates  lie  above,  but  are  shorter  than  the  outer. 


THE   EAR  53Q 

The  outer  are  called  the  phalangeal  processes,  and  by  their  union 
with  the  cells  of  Deiter,  form  the  membrana  reticularis. 

The  neuro -epithelial  cells  are  distributed  upon  the  inner  and  outer 
surface  of  the  pillar  cells.  They  are  the  hair  cells,  and  of  these  there 
are  two  rows,  inner  and  outer.  Like  the  hair  cells  of  the  preceding, 
and  the  neuro-epithelial  cells  of  the  nasal  mucous  membrane,  they 
are  about  half  the  length  of  the  sustentacular,  or  pillar  cells,  and 
are  columnar  elements  containing  a  granular  cytoplasm  and  an 
oval  nucleus.  The  outer  end  has  a  cuticular  border,  from  which 
about  twenty  hairs  extend.  The  outer  cells  are  longer  and  narrower 
than  the  inner,  and  more  numerous.  There  are  about  12,000 
outer  and  3500  inner  hair  cells.  Usually  one  hair  cell  is  present  for 
each  two  pillar  cells.  The  outer  hair  cells  are  found  in  three  or  four 
rows,  which  are  separated  by  the  ends  of  phalanges  of  Deiter's 
cells  and  the  membrana  reticularis.  The  inner  row  rests  upon  the 
outer  pillar  cells;  the  cells  of  the  next  row  lie  opposite  to  the  rods, 
and  the  third  row  alternates,  producing  a  peculiar  checker-board 
appearance,  the  ends  of  the  hair  cells  being  separated  from  one 
another  by  the  ends  of  the  Deiter  cells. 

The  sustentacular,  or  Deiter  cells  are  internal  and  external. 
Each  cell  consists  of  a  thin  pyramidal  process  and  a  large  basal 
part  that  contains  the  nucleus.  The  intercellular  spaces  of  Nuel, 
between  the  cells  of  the  organ  of  Corti,  contain  a  substance  like  that 
in  the  tunnel  of  Corti.  Internally,  Deiter's  cells  pass  through  the 
entire  layer,  and  are  continuous  with  the  cells  of  the  sulcus.  Ex- 
ternally, they  form  the  phalanges  that  help  produce  the  membrana 
reticularis.  A  surface  view  will  show  both  sustentacular  and  neuro- 
epithelium;  a  basal  view,  however,  will  show  only  sustentacular 
elements.  Just  external  to  the  Deiter  cells  are  other  sustentacular 
elements,  the  cells  of  Hensen.  These  extend  to  and  continue  with 
those  of  Claudius.  Extending  over  the  organ  of  Corti  and  arising 
from  the  upper  lip  of  the  limbus  is  a  membrane  composed  of  delicate 
fibers  and  interfibrillar  substance.  This  is  the  membrana  tectoria, 
or  Corti's  membrane.  At  one  time  this  was  part  of  the  cells  beneath, 
those  of  the  sulcus  and  auditory  teeth;  it  represents  a  cuticular 
border. 

The  divisions  of  the  auditory  nerve  are  vestibular  and  cochlear. 


540 


PRACTICAL   HISTOLOGY 


The  vestibular  arises  from  the  sacculus,  utriculus,  macula  and  the 
semicircular  canals  {cristce).  These  fibers  are  the  dendrites  of  the 
cells  in  the  ganglion  of  Scarpa  which  lies  in  the  internal  auditory 


" "  &/*& 


c 
1-2 

'-,  B 


~s. 


Z  . 

i  t 

-  _1 

O  tfi 


-    a 


o 


meatus.  The  axis  cylinders  of  these  cells  pass  to  the  oblongata. 
The  cochlear  portion  arises  mainly  in  the  cochlea,  receiving  some 
fibers  from  the  sacculus  and  posterior  semicircular  canal,  and  is 
made  up  as  follows: 


THE   EAR  54 I 

In  a  little  bony  canal  in  the  lamina  spirale  is  a  strip  of  gray  nerve 
tissue  that  is  called  the  ganglion  spirale  (Corti's  ganglion).  This 
consists  of  bipolar  cells,  one  branch,  the  dendrite  of  which  passes 
outward  into  the  organ  of  Corti,  while  the  other,  the  axis  cylinder, 
passes  through  a  minute  canal  in  the  axis  to  the  central  canal,  where 
it  meets  other  fibers  from  different  levels.  These  pass  to  the  base 
and  to  the  internal  auditory  meatus,  as  the  cochlear  branch,  and 
then  to  the  oblongata.  The  dendritic  branches  of  these  ganglion 
cells  form  a  plexus  in  the  minute  canal  of  the  spiral  shelf.  Toward 
the  organ  of  Corti  the  lamina  is  pierced  by  many  canals  called  the 
foramina  nervosa  through  which  numerous  fibers,  the  myenlinated 
dendritic  branches,  pass,  along  its  inner  epithelium,  to  the  organ  of 
Corti.  Upon  entering  these  canals,  the  myelin  sheaths  and  neuri- 
lemmas are  lost,  and  the  naked  dendrites,  in  bundles,  continue. 
Each  bundle  separates  into  two,  one  of  which  remains  at  the  inner 
surface  and  the  other  passes  along  the  outer  side  of  the  pillar  cells. 
The  latter  lies  in  the  tunnel.  Other  dendrites  cross  the  tunnel  and 
pass  to  the  outer  side  of  the  outer  pillar  cells  and  form  several  bundles 
between  the  Deiter  cells.  From  these  various  bundles,  fibrillae 
terminate  in  relation  with  the  hair  cells. 

The  blood-vessels  supplying  the  internal  ear  is  the  internal  auditory 
artery  that  passes  into  the  internal  auditory  meatus  with  the  acous- 
tic nerve.  Its  two  main  branches  are  the  cochlear  and  vestibular 
arteries.  The  cochlear  artery  gives  off  a  branch,  the  vestibulocochlear 
artery  that  sends  branches  to  the  maculae  of  the  sacculus,  the  poste- 
rior ampulla  and  neighboring  portions  of  the  posterior  semicircular 
canal,  first  part  of  the  cochlear  duct  and  utricle.  The  main  portion 
of  the  artery  passes  into  the  modiolus  and  supplies  almost  the  entire 
cochlea. 

The  vestibular  artery  supplies  the  sacculus,  utriculus  and  semi- 
circular canals;  the  capillary  plexus  is  especially  well  developed  in 
the  neuro-epithelial  areas. 

The  blood  is  collected  by  venules  that  have  a  course  that  corre- 
sponds somewhat  to  that  of  the  arteries.  The  blood  of  the  cochlear 
artery  is  carried  from  the  organ  by  the  vena  aqueductus  cochlece 
and  is  emptied  into  the  internal  jugular  vein.  Some  of  the  blood 
of  the  cochlear  artery  is  carried  by  the  internal  auditory  vein  and 


542  PRACTICAL   HISTOLOGY 

emptied  into  the  inferior  petrosal  sinus.  The  blood  of  the  ves- 
tibular artery  is  carried  by  the  vena  aqueductus  veslibuli  and  is 
emptied  into  the  superior  petrosal  sinus. 

Lymph  vessels  are  few  but  lymph  spaces  are  numerous  and  large 
in  the  internal  ear.  The  space  between  the  osseous  and  membranous 
labyrinths  is  an  extensive  lymph  space  and  contains  the  perilymph. 
This  space  communicates  with  the  subdural  lymph  space  by  peri- 
neural lymph  vessels  and  vessels  around  the  aqueductus  cochleae. 
The  membranous  labyrinth  contains  the  endolymph  and  this  can 
get  to  the  subdural  space  through  the  endolymphatic  duct  and  the 
aqueductus  vestibuli. 


CHAPTER  XX 
THE  SENSES  OF  SMELL,  TASTE,  AND  TOUCH 

THE  ORGAN  OF  SMELL 

The  nasal  mucosa  is  divided  into  respiratory  and  olfactory  por- 
tions. The  lower  portion  of  the  respiratory  area,  called  the  vestibule, 
is  lined  by  stratified  squamous  cells  to  the  turbinated  bone.  Here  a 
great  many  hairs,  sebaceous  and  mucous  glands  that  extend  for  a 
short  distance,  are  encountered.  Above  the  turbinated  bone,  the 
epithelium  is  of  the  stratified  ciliated  variety,  and  many  goblet  cells 
are  present.  The  hairs  at  the  external  meatus  are  large  and  are 
called  vibrissae.  The  tunica  propria  contains  much  lymphoid  tissue 
and  an  extensive  venous  plexus.  Mucous  and  serous  glands  are 
also  present  in  great  numbers  in  the  region  of  the  turbinated  bone 
and  nasal  septum;  they  are  largest  near  the  floor.  The  mucosa  is 
4  mm.  thick  in  this  area. 

The  olfactory  mucosa  is  usually  prominent  on  account  of  its 
yellow  color,  but  this  does  not  indicate  the  entire  olfactory  mem- 
brane. It  is  very  thick,  and  ciliated  cells  no  longer  exist.  It  lies 
in  the  superior  and  part  of  the  middle  meatus  of  the  nose  covering 
the  superior  conchal  process  and  the  nasal  septum.  The  epithelium 
is  of  three  varieties,  the  sustentacular,  neuro -epithelial  elements 
and  basal  cells. 

The  sustentacular  cells  are  irregular,  and  possess  a  peripheral 
segment  which  is  cylindrical,  and  a  basal  that  is  narrow  and  ir- 
regular. The  peripheral  segments  form  a  row  of  columnar  elements. 
The  oval  nuclei  form  a  regular  band  or  row.  The  cytoplasm 
contains  granules  and  pigment  near  the  inner  end,  the  former  being 
arranged  in  rows.  A  cuticular  border  is  present,  and  forms  the  mem- 
brana  limitans  olfactoria.  The  inner  segments  are  irregular,  and 
usually  branch  at  their  internal  ends. 

543 


544 


PRACTICAL  HISTOLOGY 


The  neuroepithelial  elements,  or  olfactory  cells,  consist  of  pe- 
culiar, inconspicuous  strips  of  protoplasm  possessing  an  enlargement 
near  the  middle,  in  which  lies  a  large,  round  nucleus.  The  latter 
form  a  band  or  zone  of  spherical  elements.  The  peripheral  ends  of 
the  rods  extend,  between  the  supportive  cells,  to  the  free  surface 


Wandering  cell. 


Excretory  duct. 


Pigment 
"*        granules. 

Oval  nucleus  of 
_      a  sustentacular 
cell. 

Round  nucleus 
of  an  olfactory 

cell. 
^H Basal  cell. 


Nerve. 


Sections  of  olfactory  glands. 

Dilated  duct. 

Fig.  295. — Vertical  Section  through  the  Olfactory  Region  of  an  Adult. 

X**400.     (Lewis  and  Stohr.) 

as  cylindrical  processes  that  project  beyond  the  surface.  The  basal 
ends  are  varicose  and  pass  to  the  basement  membrane.  This  end 
continues  through  the  basement  membrane  into  the  tunica  propria 
and  continues  as  an  amyelinated  nerve  fiber  to  the  olfactory  bulb. 
It  represents  an  axone  and  an  olfactory  cell  is  a  real  nerve  cell.  In 
the  olfactory  bulb  all  of  these  processes  terminate  in  and  form  part 
of  the  glomerular  layer. 

The  basal  cells  are  small  and  irregular  elements  that  send  processes 
between  the  upper  layers  and,  internally,  rest  upon  the  basement 


THE    SENSES    OF    SMELL,    TASTE,    AND   TOUCH 


545 


membrane.     The  cytoplasm  is  finely  granular  and  may  send    short 
processes  between  the  branches  of  the  sustentacular  cells. 

The  tunica  propria  consists  of  a  loose,  thick  network  of  fibro- 
elastic  tissue.     This  supports  the  racemose  (serous)  glands  of  Bowman 


Fig.  296. — Diagram  of  Olfactory  Mucosa. 

a,  Sustentacular  cells;  b,  neuro-epithelial  elements;  c,  basal  cells;  d,  basement 

membrane. 

whose  functionating  epithelium  possesses  a  brownish,  or  yellowish 
pigment.  These  glands  are  numerous,  forming  a  continuous  layer. 
It  also  contains  a  plexus  of  myelinated  nerve  fibers. 

The  accessory  cavities  possess  a  lining  of  ciliated  cells.     The 
mucosa  is  very  thin,  0.02  mm.,  and  it  is  firmly  attached  to  the  perios- 


GEB  ft 


"Fig.  297. — Isolated  Elements  of  the  Olfactory  Mucosa. 
a,  Neuro-epithelial  cell;  b,  sustentacular  cells  showing  cuticular  border. 

teum.     Glands  are  very  few  in  the  mucosa  of  these  cavities.     These 

cavities  comprise  the  frontal,  ethmoidal,  sphenoidal  and  maxillary 

sinuses. 

The  blood-vessels  are  numerous.     The  arterial  branches  form  a 

dense  subepithelial  plexus,  including  a  network  around  the  glands. 
35 


546  PRACTICAL  HISTOLOGY 

The  veins  are  large  in  number  and  size,  especially  upon  the  inferior 
turbinate. 

The  lymphatics  lie  in  the  lower  part  of  the  tunica  propria;  in  the 
olfactory  area,  an  extra  set  of  vessels  occurs  in  the  superficial  portion. 
These  communicate  with  the  channels  around  the  nerves. 

The  nerves  are  those  of  ordinary  and  special  sensation.  The 
former  are  derived  from  the  trigeminus  and  do  not  connect  with  the 
cells.  The  latter  form  the  olfactory  tila,  or  nerves.  The  fibers  of  the 
olfactory  nerves  are  the  axone  processes  of  the  neuro- epithelial 
elements;  these  pass  through  the  basement  membrane  to  the  tunica 
propria,  to  form  small  bundles  that  are  surrounded  by  perineural 
lymphatic  sheaths;  from  this  position  in  the  tunica  propria  they  pass 
through  the  openings  in  the  cribriform  plate  of  the  ethmoid  bone 
and  terminate  in  the  glomerular  layer  of  the  olfactory  lobe.  These 
fibers  possess  neither  myelin  sheaths  nor  neurilemma?. 

THE  SENSE  OF  TASTE 

The  sense  of  taste  is  due  to  the  taste-buds.  These  are  not  re- 
stricted to  the  circumvallate  papilla  of  the  tongue,  but  are  found  in 
the  papilla:  foliate?,  in  the  ventral  surface  of  the  epiglottis,  at  times  in 
the  fungiform  papilla?  and  in  the  soft  palate  and  uvula. 

The  organs  are  barrel-shaped,  lie  entirely  within  the  epithelial 
layer  of  the  mucosa  and  consist  of  three  kinds  of  cells,  the  sustentacular, 
gustatory  and  basal  cells. 

The  sustentacular,  or  supporting  cells  are  elongated  elements;  the 
outer  extremities  are  pointed  and  form  the  boundary  of  the  gustatory 
pore.  The  basal  extremities  are  broad  and  irregular  and  rest  upon 
the  basal  cells,  to  which  they  may  be  connected  by  delicate  proto- 
plasmic processes. 

The  gustatory  cells  are  of  the  neuro-epithelial  type.  These  are 
slender,  irregular  strips  of  protoplasm  in  which  the  large  centrally 
placed  nucleus  produces  quite  a  bulge.  The  basal  extremity  of 
each  cell  is  branched  and  connected  to  the  basal  cells  by  delicate 
protoplasmic  processes.  The  peripheral  extremity  is  continued  as 
a  delicate  hair-like  process  that  extends  into  the  epithelial  canal 
beyond  the  taste-pore  and  almost  to  the  surface  of  the  epithelium 


THE   SENSES   OF   SMELL,   TASTE,   AND   TOUCH 


547 


of  the  mucosa.     The  finely  granular  cytoplasm  contains  a  deeply 
staining,  rod-shaped  nucleus. 

The  basal  cells  are  flattened  elements  that  lie  at  the  base  of  the 
taste-bud.  The  cytoplasm  is  small  in  amount  and  extends  as  many 
processes  that  connect  with  the  other  cells  of  the  taste-bud.  The 
nucleus  contains  but  little  chromatin  and  the  cells  are  supposed  to 
be  supportive  in  function. 


1 


Fig.    298. — Section  of  a  Taste-bud  of  a       Fig.    299. — Golgi   Preparation 
Rabbit.  of  the  Nerve  Fibers  of  a 

e,  Epithelium;  p,  taste  pore  with  gustatory  Taste-bud. 

hairs;  s,  sustentacular  cells;  t,  gustatory       a,  Intragemmal  fibers;  *,  i,  Inter- 
cells;  n,  nerve  fibers.      {After  Ranvier.)  gemmal  fibers;  c,  circumgem- 

mal  fibers;    n,    nerve  fibers. 
(After  Relzius.) 

The  nerve  fibers  arise  from  the  subepithelial  plexus  of  nerve  fibers. 
These  terminal  fibers  end  in  three  ways.  Some  enter  the  organ 
{intragemmal)  where  they  divide  into  fibers  that  are  varicose  and 
end  in  knobs  between  the  neuroepithelial  cells.  Others  surround 
the  taste-bud  (cir  cum  gemmal)  and  the  fibrils  terminate  upon  the 
sustentacular  cells.  Others  terminate  between  the  epithelial  cells 
of  the  neighboring  mucosa  (inter gemmal). 


548  PRACTICAL  HISTOLOGY 

THE  SENSE  OF  TOUCH 

The  sense  of  touch  is  not  limited  to  any  special  region,  but  it  is 
best  developed  in  certain  areas,  as  the  palm  and  sole.  It  is  re- 
stricted to  the  skin,  and  represents  a  modification  of  general  sensi- 
bility. In  the  papillae  of  the  skin,  especially  that  of  the  sole  and 
palm,  are  found  the  tactile  corpuscles  of  Meissner. 

These  are  elongated  structures  that  measure  from  ioo  to  180 
microns  in  length  and  35  to  50  microns  in  diameter.  Each  consists 
of  a  capsule  of  white  fibrous  tissue  that  encloses  a  number  of  flat- 
tened masses  of  protoplasm  with  transversely  placed  nuclei.  One, 
or  more,  nerve  fibers  is  connected  with  each  organ  and  upon  contact 
with  the  corpuscle  the  neurolemma  is  lost.  The  myelin  sheath 
soon  follows  and  the  naked  axone,  after  a  spiral  course,  divides  into 
a  number  of  varicose  fibrils  that  terminate  in  small  bulbous  enlarge- 
ments near  the  capsule.  These  structures  are  found  throughout  the 
skin  but  are  most  numerous  in  the  derma  of  the  palmar  surface  of  the 
finger  tips.  They  may  be  as  numerous  as  20  to  the  square  milli- 
meter and  are  in  the  papillae  of  the  stratum  papillare,  just  beneath 
the  basement  membrane.  They  are  also  found  in  the  derma  of  the 
plantar  surface,  in  the  nipples,  lips,  glans  clitoris  and  glans  penis  and 
the  conjunctiva.  They  convey  sensations  of  pain,  pressure,  warmth 
and  cold.  It  is  said  that  two  sets  of  sensor  fibers  pass  to  them,  one 
for  light  pressure  and  slight  temperature  changes  and  the  other  for 
pain  and  extreme  temperature  changes. 

The  Pacinian  corpuscles  (Vater)  are  also  called  lamellar  corpuscles. 
Each  consists  of  a  capsule,  inner  bulb  and  end-knob.  The  capsule 
is  composed  of  a  great  number  of  lamellae  of  white  fibrous  connective 
tissue  concentrically  arranged  and  bound  together  by  an  intracap- 
sular ligament.  These  lamellae  are  from  forty  to  sixty  in  number 
and  the  outer  ones  are  more  widely  separated  from  one  another 
than  the  inner  ones.  Each  lamella  is  said  to  consist  of  both  white 
fibrous  and  yellow  elastic  tissues  and  is  covered  upon  both  surfaces 
by  endothelial  cells,  thus  forming  a  series  of  lymph  spaces. 

The  inner  bulb,  or  core  is  a  cylindrical  mass  of  protoplasm  that 
may  show  striations  and  nuclei.     It  is  thought  to  consist  externally 


THE    SENSES    OF    SMELL,    TASTE,    AND   TOUCH  549 

of  flattened  nucleated  cells  surrounding  the  more  homogeneous 
centra]  portion.  A  single  nerve  fiber  enters  each  corpuscle.  As 
it  pierce-  the  capsule  the  neurolemma  blend  with  this  and  the  mye- 
lin sheath  is  lost  when  the  inner  bulb  is  reached.  The  naked  axone, 
showing  its  fibrillation,  in  properly  stained  sections,  passes  through 
the  core  at  the  end  of  which  it  expands  into  a  knob-like  structure, 
the  cud-knob.     In  this  the  terminal  fibrils  form  a  dense  meshwork. 


Fig.  300. — Corpuscle  of  Meissner  from  Great  Toe  of  Man. 

n.    Myelinated   nerve   fiber;   h,   connective  tissue   sheath;   e,    varicosities.     The 
nuclei  are  invisible.     (Sidhr's  Histology.) 

If  the  axone  divides  in  the  core,  the  latter  also  divides.  A  small 
amyelinated  nerve  fiber  has  been  found,  by  Solokorl,  passing  to  the 
core  and  terminating  upon  it  in  a  reticular  manner. 

A  small  artery  and  vein  accompany  the  nerve  into  the  corpuscle. 
The  artery  forms  capillary  vessels  that  form  loops  between  the 
lamellae;  one  capillary  accompanies  the  nerve  and  courses  along  the 
outer  surface  of  this  for  a  variable  distance.  The  blood  is  collected 
by  a  small  vein  that  leaves  at  the  nerve  entrance. 

These  organs  are  visible  to  the  unaided  eye,  measuring  usually 
2.5  mm.  in  length  and  1  mm.  in  diameter.  They  are  found  in  the 
deep  parts  of  the  derma,  along  tendons,  around  joints,  in  the  peri- 
toneum, in  the  mesentery  (in  lower  animals)  and  in  the  pancreas 
of  the  cat. 

The  conjunctival  corpuscles,  or  bulbs  are  spherical,  oval  or  pear- 
shaped  bodies  in  which  the  cells  are  not  regularly  arranged.  The 
nerve  fiber,  upon  piercing  the  structure,  becomes  amyelinated  and 


55o 


PRACTICAL  HISTOLOGY 


passes  through  a  central  core  of  homogeneous  protoplasm  and 
terminates  in  a  bulbous  manner.  The  core  is  surrounded  by  a  capsule 
that  is  composed  of  flattened  cells.  These  organs  average  from  60 
to  400  microns  in  length  and  may  have  as  many  as  ten  nerve  fibers 
connected  with  one  organ. 


Fig.  301. — A  Tactile  Corpuscle 
with  its  Cells  and  Ter- 
minal Neurofibrils. 

a.  Axone.     (After  Van  de  Velde.) 


Axis  cylinder. 


Inner  core. 


Capsules. 


Nerve  fiber. 
Artery. 

Fat  cells. 


Fig.  302. — Small  Lamellar  Corpuscle 
from  the  Mesentery  of  a  Cat.  X  50. 

The  nuclei  of  the  capsule  cells  appear  as 
thickenings.  The  myelin  of  the  nerve 
fiber  may  be  traced  to  the  inner  core 


The  genital  corpuscles,  or  bulbs  are  more  complex.  Each  is 
divided  into  two  to  six  knob-like  parts.  The  nerve  fiber  enters 
the  organ  and  divides  into  numerous  branches  each  of  which  passes 
to  a  segment;  here  it  may  continue  undivided  or  form  a  series  of 
branches.  These  are  surrounded  by  the  capsular^  cells.  These 
organs  measure  from  60  to  400  microns  in  length  and  40  to  100  mi- 
crons'in  diameter.  They  are  found  in  the  mucosa  of  the  glans  penis 
andVans  clitoris  and  neighboring  structures. 


CHAPTER  XXI 
DEVELOPMENT  OF  FACE  AND  TEETH 

The  development  of  the  face  is  a  complicated  process,  a  number 
of  different  fetal  structures  taking  part  therein.  Just  after  the  forma- 
tion of  the  head-fold  of  the  amnion  there  is  an  area,  just  precephalad 
to  this  groove,  in  which  the  ectoderm  and  entoderm  are  in  contact. 
This  is  the  buccopharyngeal  area.  As  the  head-fold  of  the  amnion 
advances  this  buccopharyngeal  area  is  folded  ventral  so  as  to  form 
the  ventral  part  of  the  blunt-head  process  (see  Fig.  230,  A,  and  C,  p. 
400).  By  this  time  this  area  has  become  a  depression,  the  oral 
depression,  or  stomodeum,  the  floor  of  which  is  the  buccopharyngeal 
membrane.  This  depression  is  present  at  about  the  twelfth  day 
of  intrauterine  life.  The  floor  of  this  depression  sinks  deeper  and 
the  margins  become  more  pronounced. 

At  about  the  fifteenth  day  the  lower  boundary  of  the  depression 
becomes  formed  upon  each  side  into  a  finger-like  process,  called 
the  first  branchial  arch,  that  soon  divides  into  a  shorter  upper  portion, 
the  maxillary  division,  and  a  lower  part,  the  mandibular  division. 
The  upper  division  forms  now  the  lateral  boundary  and  the  lower 
the  inferior  boundary  of  the  oral  depression.  At  about  the  same 
time  the  tissues  in  the  frontal  region  become  projected  in  the  form 
of  a  blunt  mass  between  the  maxillary  divisions  of  the  first  arch, 
constituting  the  nasofrontal  proccess.  Thus  the  stomodeum  has 
become  a  pentagonal  fossa.  At  about  the  eighteenth  day  a  second 
finger -like  process  makes  its  appearance  beneath  the  mandibular  por- 
tion of  the  first  arch;  this  is  followed  by  a  third  arch  about  the 
twenty-first  day,  a  fourth  by  about  the  twenty-fourth  day,  and  the 
fifth  and  last  arch  is  formed  by  the  twenty-eighth  day.  The  last 
are  less  highly  developed  than  the  first,  and  while  the  lower  ones 
are  forming  the  upper  ones  are  undergoing  metamorphosis  into 
their  adult  structures. 

55i 


552  PRACTICAL   HISTOLOGY 

The  changes  that  occur  in  the  branchial  arches  will  be  considered 
first:  Each  arch  consists  of  a  core  of  mesoderm  containing  a  rod  of 
cartilage  and  a  blood-vessel  called  the  branchial  arch  vessel;  externally 
the  arch  is  covered  by  ectoderm  and  internally  by  entoderm.  The 
arches  are  separated  from  each  other  by  a  groove  or  depression, 
internally,  and  externally,  and  spanning  the  groove  is  the  visceral 
cleft  membrane  consisting  merely  of  ectoderm  and  entoderm,  so  that 
no  real  complete  cleft  exists  in  the  early  stages  of  development; 
in  aquatic  animals  these  membranes  do  rupture  to  form  the  gill- 
clefts.  On  each  side  there  are  four  external  and  four  internal  vis- 
ceral grooves  or,  better,  branchial  pouches. 

The  first  arch,  as  previously  mentioned,  divides  into  two  portions, 
maxillary  and  mandibular;  the  maxillary  part  unites  with  nasofrontal 
process  to  complete  the  upper  jaw;  it  itself  gives  rise  to  the  bulk  of 
the  maxilla  and  most  of  the  palate.  The  upper  jaw  is  completed  by 
about  the  fortieth  to  the  forty-second  day.  The  mandibular 
process  unites  with  its  fellow  of  the  opposite  side  to  form  the  entire 
mandible,  union  being  completed  by  the  end  of  the  fifth  week,  or 
thirty-fifth  day.  In  addition,  the  cartilage  of  the  mandibular 
process  gives  rise  to  incus  and  malleus,  and  stylomandibular  ligament. 

The  rod  of  cartilage  of  the  second  arch  gives  rise  to  the  stapes, 
styloid  process,  stylohyoid  ligament  and  lesser  cornu  of  the  hyoid 
bone. 

The  cartilage  of  the  third  arch  forms  the  body  and  greater  cornu 
of  the  hyoid  bone. 

The  cartilage  of  the  fourth  and  fifth  arches  unite  and  form  a  single 
mass,  the  thyroid  cartilage  of  the  larynx. 

The  first  external  branchial  pouch  persists  only  at  its  dorsal 
end  to  form  here  the  external  auditory  canal.  From  both  first 
and  second  arches  in  this  region  the  pinna  of  the  ear  is  developed. 
The  remaining  pouches  are  lost  as  the  arches  overlap  each  other 
from  above  downward.  Occasionally  part  of  a  pouch  persists  as  an 
enclosed  cyst  of  ectoderm  and  this  is  called  a  branchial  cyst.  In  case 
a  pouch  membrane  ruptures  and  permits  of  a  passage-way  from  the 
outside  to  the  pharynx  it  is  called  a  congenital  cervical  fistula. 

The  first  internal  pouch  is  formed  into  a  tube  with  its  outer  end 
dilated  into  an  irregular  cavity,  the  tympanic  cavity;  the  tube-like 


DEVELOPMENT  OF  FACE  AND  TEETH  553 

portion  connecting  this  with  the  pharynx  is  called  the  auditory 
tube.  That  part  of  the  first  pouch  membrane  separating  the  external 
auditory  canal  from  the  tympanic  cavity  is  the  future  tympanic 
membrane,  or  ear  drum.  In  the  middle  of  the  ventral  portion  of  the 
first  pouch  is  found  a  projection,  the  Htbereulum  impar,  which  later 
becomes  the  anterior,  or  apical  two-thirds  of  the  tongue. 

From  the  region  of  the  second  pouch  (representing  the  ventral 
ends  of  the  second  and  third  arches)  we  find  the  tonsil  and  lateral 


Fig.    303. — Face  of  an  Embryo  of  8  mm.      {McMurrich,  after  His.) 
pg,  Globular  (median  nasal)  process  of  nasofrontal  process;  np,  nasal  pit  bounded 
externally  by  the  lateral  nasal  process;  os,  oral  pit;  mxp,  maxillary  process  of 
first  branchial  arch. 


recess  of  the  pharynx  developed,  dorsally,  while  ventrally  in  the 
median  line  the  entire  of  the  thyreoid  body  is  formed,  and  just  lateral 
of  this  the  dorsal,  or  basal  one-third  of  the  tongue  by  two  masses 
(one  on  each  side). 

In  the  third  pouch  region  (third  and  fourth  arches)  the  thymus 
body,  as  two  lobes,  appears  and  also  the  superior  parathyreoids. 

From  the  fourth  pouch  (fourth  and  fifth  arches)  the  lateral 
thyreoids,  or  postbranchial  bodies  and  the  inferior  parathyreoids. 


554  PRACTICAL  HISTOLOGY 

The  nasofrontal  process  is  at  first  a  blunt  mass  of  tissue  pro 
jecting  from  the  frontal  region.  As  it  grows  down  between  the 
maxillary  divisions  of  the  first  visceral  arch,  it  becomes  thickened 
along  its  margins,  forming  here  the  median  nasal  processes;  each 
process  contains  a  little  depression  that  constitutes  the  nasal  pit. 
In  addition,  two  masses,  the  lateral  nasal  processes,  develop  from  the 
nasofrontal  process,  at  the  orbital  region,  to  form  the  lateral  boundary 
of  the  nasal  pits.  Usually  by  the  fortieth  or  forty-second  day 
the  nasofrontal  process  has  filled  the  gap  between  the  two  max- 
illary processes  of  the  first  arch,  and  union  of  these  parts  is  com- 
pleted. As  a  result  the  nasal  pits  are  separated  from  the  mouth 
cavity.  The  derivatives  of  the  nasofrontal  process  are  the  middle 
of  the  upper  jaw  (intermaxillary  bones),  the  middle  of  the  upper 
lip,  the  tip,  septum,  alae  and  bridge  of  the  nose  and  the  vomer.  The 
crevice  between  lateral  nasal  processes  and  the  maxillary  division 
of  the  first  arch  extends  from  the  orbit  of  the  nose  cavity.  When 
this  crevice  is  closed  a  cord  of  epithelium  is  inclosed,  and  by  hollowing 
out  this  cord  of  cells  forms  the  nasolacrimal  duct.  If  the  lip  portions 
of  the  nasofrontal  process  and  first  arch  fail  to  unite,  a  malformation, 
unilateral,  or  bilateral  hare-lip,  is  produced.  If  the  bony  parts  within 
are  affected,  various  forms  of  cleft-palate  result. 

The  palate  is  developed  in  the  form  of  three  shelves,  two  lateral 
from  the  maxillary  processes  of  the  first  arch  and  one  frontal,  tri- 
angular, from  the  nasofrontal  process. 

At  about  the  eighth  week  union  between  the  lateral  shelves  at  the 
front  end  and  the  nasofrontal  portions  begin;  by  the  ninth  week 
union  as  far  as  the  posterior  border  of  the  future  hard  palate  is  com- 
pleted, by  the  eleventh  week  the  soft  palate  is  finished  and  by  the 
end  of  the  third  month  the  uvula  is  complete.  Various  malforma- 
tions may  occur  here,  as  partial,  or  complete  cleft-palate  and 
bifid  uvula.  Then  after  the  upper  jaw  is  completed  two  ridges 
appear  upon  each  jaw,  the  inner  represents  the  gum  and  the  outer 
the  lip. 

The  Teeth. — The  teeth  are  developed  partially  (enamel)  from  the 
ectoderm  and  partially  (dentin,  cementum,  pulp,  and  peridental 
membrane)  from  the  mesoderm. 

There  are  two  sets  of  teeth  in  the  mammals,  temporary,  or  de- 


DEVELOPMENT  OF  FACE  AND  TEETH 


555 


ciduous,  or  milk  teeth,  and  permanent,  or  succedaneous  teeth. 
Such  animals  are  dipkyodonts.  Animals  that  may  develop  teeth 
successively  without  regard  to  number  are  polyphyodonts. 

In  the  former  case  the  teeth  are  unlike,  and  the  animals  are  heter- 


Fig.  304. — Four  Stages  of  Tooth  Development. 
(After  B'ohm,  Davidoff  and  Huber.) 
A,  Formation  of  the  enamel  from  the  dental  shelf;  B,  later  stage  with  early 
formation  of  the  dental  papilla;  C,  later  stage  showing  enamel  sac  with 
its  layers  differentiating  and  the  dental  papilla  well  advanced;  D,  enamel 
sac  completed  (just  preceding  enamel  formation)  connected  to  dental 
shelf;  dental  papilla  completed.  I,  I,  I,  I.  oral  epithelium;  2,  2,  2,  2, 
basal  layer  of  same;  3,  3,  3,  3,  mesoderm  of  jaw;  4,  4,  4,  4,  outer  layer  of 
enamel  organ;  5,  5,  5,  5,  middle  layer;  6,  6,  6,  inner  layer;  7,  7,  7,  dental 
papilla;  8,  layer  of  odontoblasts;  9,  dental  shelf;  10,  follicular  sheath. 


556  PRACTICAL   HISTOLOGY 

odonts,  while  in  the  latter  case  the  teeth  are  all  alike  and  the  class 
is  that  of  homodonts. 

The  teeth  begin  to  develop  during  the  sixth  week  (shortly  after 
the  completion  of  the  lower  jaw).  From  the  under  surface  of  the 
thickened  epithelium  of  the  jaw  a  band  of  epithelial  cells  grows  into 
the  mesodermal  core  of  the  jaw.  This  is  the  dental  shelf,  the  earliest 
indication  of  the  developing  teeth.  Shortly  after  the  formation  of 
this  shelf  the  epithelium  at  the  area  of  thickening  sinks  in  forming 
the  dental  groove.  The  dental  shelf  extends  from  one  end  of  the 
jaw  to  the  other  and  leans  toward  the  median  plane  of  the  head, 
and  from  the  outer  free  or  labial  surface  ten  little  germs  or  buds 
develop,  called  the  enamel  germs.  There  are  ten  in  each  jaw,  and 
they  represent  enamel  organs  of  the  temporary  teeth.  These  buds 
appear  successively:  those  for  the  central  incisors  first,  then  lateral 
incisors,  first  molars,  canine,  and  second  molars.  The  earliest  buds 
appear  during  the  seventh  or  eighth  week.  The  enamel  bud  is 
at  first  flask-shaped,  and  its  connection  with  dental  shelf  becomes 
smaller.  Gradually  the  surface  opposite  to  the  dental  shelf  con- 
nection becomes  invaginated  by  condensing  mesoderm;  the  concavity 
deepens  and  a  sac  is  thus  formed,  while  at  the  same  time  the  dental 
shelf  connection  becomes  more  attenuated.  The  sac  consists  of 
three  layers,  inner,  middle,  and  outer.  The  mass  of  condensed  meso- 
derm that  has  caused  the  sac  formation  of  the  enamel,  but  which 
lies  now  in  the  enamel  sac,  constitutes  the  dental  papilla.  During 
about  the  tenth  week  mesoderm  in  the  immediate  neighborhood  of 
the  enamel  sac  condenses  to  form  a  sheath  for  the  whole  structure, 
and  this  is  called  the  dental  follicle.  Meanwhile  the  dental  shelf 
becomes  attenuated  and  tends  to  disappear. 

The  succeeding  changes  will  be  described  under  Enamel  Forma- 
tion, Dentin  Formation  and  Cementum  Formation. 

Enamel  Formation. — The  enamel  organ  now  consists  of  three 
la  vers:  the  outer  layer  is  composed  of  simple  columnar  epithelial 
cells  continuous  with  the  inner  layer  of  cells  at  the  base  of  the  organ. 
They  plav  no  part  in  the  formation  of  enamel.  The  middle  layer 
consists  of  a  mass  of  stellate  cells  varying  in  thickness  as  Fig.  304 
shows;  these  cells  make  up  the  bulk  of  the  enamel  organ  and  the 
meshwork  formed  bv  them  is  filled  with  a  fluid.     This  layer  likewise 


DEVELOPMENT  OF  FACE  AND  TEETH 


557 


has  nothing  to  do  with  the  direct  formation  of  enamel,  but  seems  to 
have  a  nutrient  function.  Along  the  innermost  portion  of  this 
reticular  mass  is  a  group  of  cells  forming  a  layer  called  the  stratum 
intermedium.  This  layer  consists  chiefly  of  spherical  cells  mixed 
with  some  columnar  elements.     Apparently  the  spherical  cells  have 


Fig.  305. — Section  of  a  Developing  Tooth  of  a  Cat  Embryo. 

(After  Pier  sol.) 
A,  Outer,  B,  middle,  C,  inner  layers  of  enamel  organ;  D,  formed  enamel;  E, 
formed  dentin;  F,  layer  of  odontoblasts;  G,   follicular  sheath;   H,   dental 
papilla,  mesoderm. 

elongated  to  the  columnar  type,  probably  for  the  purpose  of  re- 
placing cells  that  fail  in  the  innermost  layer.  This  stratum  inter- 
medium is  looked  upon  as  the  reverse  layer  to  the  enamel-forming 
cells;  the  cells  of  this  stratum  are  most  numerous  where  enamel 
formation  is  most  active. 


558  PRACTICAL  HISTOLOGY 

The  inner  layer  is  composed  of  a  single  row  of  tall  slender,  col- 
umnar elements;  these  form  a  closely  packed  unbroken  layer  sur- 
rounding the  dental  papilla  and  are  termed  the  ameloblasts.  The 
nuclei  lie  in  the  peripheral  portion  of  the  cells. 

Enamel  deposition  begins  during  the  sixteenth  week  of  intrauterine 
life,  in- the  temporary  teeth.  According  to  Tomes  and  others,  the 
inner  ends  of  the  enamel  cells  become  calcified  and  converted  di- 
rectly into  enamel.  An  organic  matrix  is  formed  in  which  the  enamel 
is  deposited,  probably  in  the  form  of  calcoglobulin  globules.  The 
organic  matter  disappears,  leaving  the  homogeneous,  inorganic  mate- 
rial representing,  no  doubt,  the  fused  globules  of  calcoglobulin. 
According  to  Andrews  and  others,  the  enamel  is  secreted  from  the 
cell  in  some  form  (calcoglobulin),  and  this  solidifies  and  forms 
outside  of  the  cell.  The  first,  however,  seems  to  be  the  more  accepta- 
ble explanation.  Enamel  is  formed  from  within  outward,  so  that 
the  youngest  enamel  is  upon  the  surface  while  the  oldest  is  next  to 
the  dentin. 

Capillary  blood-vessels  have  been  noted  in  the  enamel  organ  by 
Bromell.  It  seems  that  before  calcification  begins  that  vessels 
are  absent;  with  the  formation  of  enamel  vascularization  of  the 
enamel  organ  begins  and  is  said  to  persist  until  the  tooth  erupts. 
By  the  time  that  the  tooth  begins  to  erupt,  or,  at  the  latest,  when 
completely  erupted,  the  enamel  is  fully  formed. 

Between  the  enamel  organ  and  the  surface  of  the  dental  papilla 
is  a  layer  of  homogeneous  substance  called  the  membrana preformativa. 
Reference  to  this  will  be  made  later. 

Dentin  Formation. — The  dentin  is  derived  from  the  dental  papilla; 
this  structure  is  composed  of  embryonic  connective  tissue  in  which 
four  different  kinds  of  cells  are  found.  Upon  the  surface  of  the 
papilla  will  be  found  a  single  layer  of  flask-shaped  cells,  the  odon- 
toblasts. These  form  the  membrana  eboris  from  which  the  dentin 
is  derived.  The  basal  portion  of  each  cell  is  directed  toward  the 
papilla,  or  centrally,  and  contains  the  nucleus.  Each  cell  possesses 
processes;  those  which  are  directed  toward  the  enamel  organ  con- 
stitute the  ultimate  dental  fibers.  These  cells  are  differentiated 
shortly  before  the  formation  of  dentin  begins.  Just  beneath  the 
layer  of  odontoblasts  the  papilla  is  practically  devoid  of  cells;  beneath 


DEVELOPMENT  OF  FACE  AND  TEETH 


559 


this,  however,  there  is  a  cellular  area  of  mixed  cells  and  then  again 
a  central  area  containing  but  few  cells. 

Dentin  is  first  formed  at  the  cutting,  or  occlusal  surface  and  during 
the  sixteenth  week  of  intrauterine  life.     The  dentin  seems  to  be  a 
retion  from  the  peripheral  ends  of  the  odontoblasts  so  that  the 
processes  in  this  region  are  surrounded  by  the  lime  salts,  thus  form- 
ing the  dental   sheaths  and   tubules;  the   odontoblasts   are   always 


Enamel 

Enamel  membrane 

Dentin 
Dental  papilla 


Fig.  306. — Longitudinal  Section  of  a  Developing  Tooth. 
a,   Bone  of  the  alveolar  process.      (Photograph.     Obj.  32  mm.) 

beyond  the  area  of  dentin  formation.  The  dentin  is  laid  down  from 
without  inward,  and  in  areas  where  dentin  formation  is  incomplete 
spaces,  that  are  called  the  interglobular  spaces,  remain.  As  the  dentin 
becomes  thicker  (by  encroachment  upon  the  dental  papilla)  the 
dental  fibers  elongate  and  the  tubules  become  correspondingly 
longer.  The  dentin  in  the  crown  portion  is  formed  first,  the  root 
portion  being  completed  last.  When  the  teeth  begin  to  erupt  their 
roots  are  partially  formed;  by  the  time  that  the  whole  crown  is 
exposed  the  fang  is  usually  completed.     In  the  case  of  the  incisor 


560  PRACTICAL  HISTOLOGY 

teeth  the  roots  are  usually  completed  by  the  time  that  the  tooth 
begins  to  erupt. 

Cementum  Formation. — The  cementum  is  also  of  mesodermal 
origin.  As  the  enamel  organ  becomes  invaginated  by  the  dental 
papilla  the  mesoderm  immediately  surrounding  the  enamel  organ 
condenses  to  form  a  sac-like  covering,  the  dental  follicle.  This 
structure  gives  rise  to  the  cementum  and  the  alveolar  process  of  the 
jaw  and  its  remains  constitute  the  peridental  membrane.  The 
follicle  is  formed  shortly  after  the  tenth  week.  During  the  earlier 
stages  of  development  the  dental  follicle  covers  the  entire  enamel 
organ  and  is  connected  with  the  dental  papilla  at  its  base.  The 
follicle  upon  its  outer  surface  forms  bone,  and  upon  its  inner  surface 
orms  the  cementum  of  the  tooth.  As  the  enamel  organ  grows  the 
follicle  seems  to  recede  from  the  cutting  edge  until  the  neck  portion 
is  reached;  at  this  point  it  remains,  and  as  the  root  is  formed  by  the 
dental  papilla  the  follicle  forms  the  cementum  until  the  full  length 
of  the  root  is  reached.  The  process  of  cementum  formation  is  like 
that  of  bone,  a  secretion,  and  layers  are  formed  as  described  in  the 
section  on  the  structure  of  cementum.  The  cementum  and  bone 
of  the  jaw  are  developed  from  the  dental  follicle,  or  peridental  mem- 
brane, at  the  expense  of  the  latter,  it  becoming  thinner  as  the  cemen- 
tum and  alveolar  bone  increase  in  thickness. 

The  temporary  teeth  begin  to  erupt  from  the  sixth  to  the  eighth 
month  after  birth  and  the  set  is  usually  completed  by  the  twenty- 
fourth  to  the  thirtieth  or  thirty-sixth  month.  The  order  of  eruption 
is  as  follows : 

Central  incisors,  sixth  to  eighth  month. 

Lateral  incisors,  seventh  to  ninth  month. 

First  molars,  twelfth  to  fourteenth  month. 

Canines,  sixteenth  to  eighteenth  month. 

Second  molars,  twenty-fourth  to  thirty-sixth  month. 

The  permanent  teeth  are  thirty-two  in  number.  The  difference 
in  number  of  the  two  sets  and  later  appearance  of  added  teeth  is  due 
to  the  fact  that  the  jaw  at  certain  periods  will  accommodate  only 
a  certain  number  of  teeth,  and  any  attempt  to  hurry  their  appearance 
will  interfere  with  the  dental  arch.     Of  these  permanent  teeth,  the 


DEVELOPMENT  OF  FACE  AND  TEETH 


56l 


molars,  twelve  in  Dumber,  are  not  succedaneous  teeth  at  all,  but 
primary  teeth  as  will  be  explained  later.  The  germs  for  most  of  the 
permanent  teeth  are  formed  during  intrauterine  life. 

During  the  sixteenth  week  a  bud  appears  at  each  end  of  the  dental 
shelves;  these  buds  are  the  germs  for  the  first  permanent  molar  teeth. 
During  the  seventeenth  week  the  germs  for  the  central  incisors  appear 
from  the  Ungual  surface  of  the  dental  shelf,  opposite  the  point  of 


Fig.  307. — Section  of  Jaw  showing    the    Temporary  (a)   and  Permanent 
(b)  Tooth  Germs.     (Photograph.     Obj.  32  mm.,  oc.     5  x.) 

formation  of  the  corresponding  temporary  tooth;  the  remaining  suc- 
cedaneous teeth  follow  in  order  of  their  eruption.  The  enamel 
organs  undergo  the  same  changes  as  previously  described,  with  the 
exception  that  the  process  is  somewhat  slower,  making  their  eruption 
somewhat  later.  As  was  stated  above,  the  germs  for  the  first  perma- 
nent molars  appear  at  the  ends  of  the  dental  shelves  and  so  have  no 
forerunners;  the  germs  for  the  second  molars  are  developed  from  the 

36 


562  PRACTICAL  HISTOLOGY 

neck  of  the  enamel  organs  of  the  first  molar  during  the  third  to  the 
fifth  month  after  birth;  the  enamel  sacs  for  the  third  permanent 
molars  appear  from  the  neck  of  the  enamel  sacs  of  the  second  molars 
during  the  third  to  the  fifth  year  after  birth.  All  of  the  molar  teeth, 
therefore,  have  no  predecessors,  and,  are  then,  primary  and  not  suc- 
cedaneous  teeth. 

The  first  permanent  molar  tooth  is  the  first  one  of  the  second  set 
to  appear;  the  order  and  times  are  as  follows: 

First  molar,  sixth  year. 

Central  incisors,  seventh  year. 

Lateral  incisors,  eighth  year. 

First  premolars ,  ninth  year. 

Second  premolars,  tenth  year. 

Canines,  eleventh  to  twelfth  year. 

Second  molars,  twelfth  to  thirteenth  year. 

Third  molars,  seventeenth  to  twenty-fifth  year. 

The  eruption  and  succession  of  the  teeth  are  by  no  means  simple 
processes.  As  the  tooth  germs  develop  they  at  first  lie  in  a  groove  of 
the  jaw,  covered  merely  by  the  gum;  gradually  transverse  partitions 
of  bone  form  so  that  the  entire  tooth  is  ultimately  incased  in  the 
bone  of  the  jaw.  The  bone  intervening  between  the  tooth  and  the 
gum  amounts  to  but  a  thin  lamella  that  is  completed  shortly  before 
the  tooth  is  to  erupt,  except  in  the  region  where  the  gubernaculum 
passes  to  the  gum.  As  eruption  is  to  take  place,  that  bone  which  is 
last  formed  (over  the  cutting  edge)  is  resorbed  so  that  there  is  no 
interference  with  eruption. 

The  process  of  eruption  is  as  follows:  The  bone  covering  the 
labial  surface  of  the  crown  is  resorbed  until  fully  one-half  of  the 
surface  is  exposed;  this  is  followed  by  the  resorption  of  the  bone  on 
the  lingual  surface  but  here  the  process  is  slower  and  less  complete, 
leaving  some  bone  to  protect  the  germs  of  the  permanent  teeth 
underneath.  As  a  result  of  this  process  the  crown  apparently  grows 
through  the  gum  when  in  reality  the  gum  becomes  stretched  over 
the  tooth  by  the  disappearance  of  the  bone  beneath.  As  the  resorp- 
tion continues  until  the  crown  is  exposed,  new  bone  is  laid  down 
about  the  base  of  the  tooth  to  strengthen  its  position.     According 


DEVELOPMENT  OF  FACE  AND  TEETH         563 

to  some  writers  the  tooth  erupts  by  the  growth  of  the  root  forcing 
the  crown  above  the  gum  surface.  When  one  considers  that  in  the 
temporary  and  permanent  incisor  teeth  the  roots  are  completed  by 
the  time  eruption  occurs,  this  force  cannot  be  counted  upon  as  a 
factor  in  the  eruption  of  the  teeth.  It  might  play  some  part  in  the 
eruption  of  the  other  teeth,  but  even  this  is  doubtful. 

From  the  eruption  of  the  second  temporary  molar  tooth  until  the 
fourth  year  the  teeth  are  practically  quiescent.  From  the  fourth 
year  on  the  temporary  teeth  begin  to  decalcify  and  drop  out  to 
make  room  for  the  permanent  teeth.  The  process  of  decalcification 
is  one  of  absorption;  it  begins  in  the  apical  portion  of  the  tooth  and 
advances  to  the  enamel  line.  The  central  incisors  are  the  first 
affected,  at  about  the  fourth  year,  and  the  others  follow  in  order  of 
their  eruption.  As  a  result  of  this  process  the  root  becomes  absorbed 
and  the  hold  of  the  tooth  upon  the  jaw  becomes  weakened;  ulti- 
mately merely  an  enamel  cap  remains;  this  process  extends  over  a 
period  of  about  three  years  for  each  tooth,  going  on  simultaneously 
or  successively  in  the  various  teeth.  Some  claim  that  the  process  of 
resorption  of  the  roots  is  due  to  the  pressure  exerted  upon  the  root 
by  the  permanent  tooth  beneath.  This  does  not,  however,  seem 
to  be  the  cause,  for  in  cases  of  absence  of  the  succedaneous  tooth  the 
process  of  absorption  of  the  root  of  the  temporary  tooth  occurs  as 
usual. 

The  permanent  teeth  follow  the  temporary  successively  as  the 
latter  are  lost.  As  the  jaw  gradually  increases  in  length  there  is  a 
second  permanent  molar  added  at  the  twelfth  to  the  fourteenth  year 
and  a  third  one  at  the  eighteenth  to  the  twenty-fifth  year. 

The  permanent  teeth  erupt  in  the  same  manner  as  the  temporary 
organs;  that  is,  by  the  absorption  of  the  bone  from  the  crown  portion. 
As  this  process  of  absorption  occurs  during  the  eruption  of  both  sets 
the  jaws  would  become  thinner  from  above  downward;  to  offset  this 
nature  adds  below  more  than  is  absorbed  above  so  that  the  dimen- 
sion from  above  downward  increases  up  to  the  prime  of  life.  As  the 
second  set  is  gradually  lost  bone  is  not  replaced  as  rapidly  as  lost 
so  that  in  an  old  jawr  the  alveolar  processes  are  lost  (showing  the 
absorption  from  above  downward)  and  the  vertical  dimension 
decreases. 


564  PRACTICAL  HISTOLOGY 

Connected  with  the  permanent  tooth  is  a  structure,  the  guber- 
naculum  dentis,  that  seems  to  be  of  importance.  It  is  a  fibrous, 
cord-like  structure  attached  to  the  apex  of  the  tooth-sac  and  ends 
at  the  epithelium  of  the  gum.  It  seeme  to  direct  the  follicle  by  its 
tension  and  also  to  indicate  the  direction  of  eruption,  and  to  main- 
tain the  tooth  in  position. 

In  regard  to  malformation  of  the  teeth,  both  sets  may  fail  to  appear, 
or  the  succedaneous  teeth  alone  may  not  develop;  again  individual 
teeth  may  be  absent,  or  a  third  set  may  appear  after  the  second  has 
been  lost.  What  is  more  common  than  the  latter  is  a  duplication 
of  some  of  the  permanent  teeth  forming  a  row  within  the  normal  set; 
a  fourth  molar  may  appear  if  the  jaw  is  long  enough  to  accommodate 
it.  Wisdom  teeth  are  frequently  absent.  Malformations  of  the 
root  may  be  in  the  form  of  an  additional  root  or  the  fusion  of  several 
to  form  one  massive  root.  Again,  the  teeth  may  be  united  by  fusion 
(if  before  birth)  or  concrescence  (if  after  birth).  If  two  teeth  are 
found  in  a  single  sac  the  condition  is  known  as  geminous  teeth. 


INDEX 


Absorption,  87 

of  fats,  273 

of  proteins,  273 

of  sugars,  273 
Accessory  nasal  cavities,  307 

tear  gland,  521 
Acervulus  cerebri.  492 
Achromatin,  62 
Adenoids,  307 
Adipose  tissue,  in 
Adrenal,  346 
Afferent  arteriole,  333 
Agminated  nodule,  271 
Albumen,  Mayer's,  53 
Alcohol,  9 

absolute,  9 

absolute  and  ether,  10,  13,  42 

absolute  and  formalin,  10,  42 
Alimentary  tract,  233 
Alveolar  ducts,  315 
Alveolodental  membrane,  244 
Alveoli  of  lung,  316 
Alveus  of  lung,  316 
Ameboid  movement,  65 
Ameloblast,  558 
Amitosis,  67 
Amnion,  407 
Amniotic  folds,  400 
Ampullae,  200 
Amyloid  bodies,  369 
Anastomoses,  200 
Anterior  ciliary  arteries,  519 
Antrum,  tympanic,  527 
Anus,  276  , 
Aorta,  i95j 


Aortic  bodies,  213 

valves,  188 
Appendages  of  eyeball,  520 

of  skin,  419 
Appendices  epiploicae,  275 
Appendix,  276 
Aqueductus  cerebri,  469 
Aqueous  humor,  515 
Arched  connecting  tubules,  331 
Arcuate  fibers,  453,  462 

nucleus,  462 
Areola,  433 
Areolar  tissue,  103 
Arachnoid,  435 
Arrector  pili  muscle,  425 
Arterial  arcade,  333 
Arteries,  large,  195 

medium,  192 

small,  196 
Arteriolar  recta;,  335 
Artery,  changes  in  old  age,  196 

difference  in  functions,  196 
Astrocytes,  167 
Astrosphere,  63 
Attic,  527 

Attraction  sphere,  63 
Auditory  nerve,  539 

teeth,  537 

tube,  530 
Axilemma,  161 

Axis-cylinder  hillock,  157,  161 
Axone,  161 

B 

Balsam,  35 

Basement  membrane,  86 


565 


566 


INDEX 


Belly-stalk,  399,  403 
Bile,  capillary,  284 

ducts,  293 
Bladder,  340 
Blind  spot,  512 
Blocking,  12 
Blood,  clotting,  210 

composition  of,  203 

fixation,  42,  44,  45,  46 

platelets,  210 

shadows,  210 

spreads,  42 

stains,  43,  45,  46 

technic,  41 
Blood  cell,  counting,  44 

crenated,  210 

origin  of,  213 

platelet,  209 

red,  203 

white,  206 
Bone,  120 

cancellous,  124 

compact,  124 

composition,  121 

development,  endochondral,  133 
intramembranous,  136 

endosteum,  127 

Haversian  canals,  125 
lamellae,  125 
systems,  125 

Howship's  lacunae,  125 

lacunae,  126 

lamellae,  124 

lamellar  fibers,  122 

marrow,  red,  127 
yellow,  127 

ossification,  133 

osteoblasts,  122 

osteoclasts,  131 

periosteum,  121 

regeneration,  138 

Sharpey's  fibers,  122 

structure,  121 
Bowman's  capsule,  326 


Bowman's  glands,  545 

membrane,  497 
Brachia,  456 

conjunctiva,  454,  457 

pontis,  454,  457 
Brain,  451 

internal,  anatomy  of,  458 

stem,  452 
Branchial  arches,  551 

derivatives  of,  552 
Bronchi,  311 
Bronchiole,  314 

respiratory,  313 
Brown  striae  of  Retzius,  239 
Bruch,  membrane  of,  500 
Bruecker's  lines,  141 
Buccopharyngeal  membrane,  551 
Bulbourethral  glands,  370 


Calix  major,  336 

minor,  336 
Callosum,  458 
Canal  of  Schlemm,  504 

of  spinal  cord,  444 
Canaliculus,  525 
Canalized  fibrin,  407 
Capillary,  198 
Capsule  of  Glisson,  283 

of  Tenon,  495 
Cardiac  glands,  259,  262 

lower,  257 

upper,  257 
Cardiac  muscle,  150 
Cartilage,  117 

articular,  119 

cells,  117 

chondroblasts,  117 

elastic,  120 

fibro,  120 

hyalin,  118 

of  Santorini,  309 

of  Wrisberg,  309 


INDEX 


567 


Cartilage,  sympliysial,  120 

white  iibro,  120 
Caruncle,  523 
Casein,  432 
Cauda  equina,  440 
Cedar  oil,  11,  33 
Cell  body,  58 

contents,  59 

knot,  406 

mass,  inner,  73 
outer,  73 
Cell,  58 

parts,  58 

structure,  58 

wall,  64 
Cells,  acid,  261 

adelomorphous,  259 

arrangement  of,  in  the  brain  stem, 

459 
centro-acinar,  298 

ciliated,  81 
simple,  81 
stratified,  82 
clasmocytes,  104 
columnar,  simple,  80 

stratified,  81 
connective  tissue,  104 
decidual,  407 
endothelial,  89,  90 
ependymal,  166 
ganglion,  174,  176 
glandular,  84 
goblet,  83 
gustatory,  546 
hepatic,  286 
lamellar,  104 
Langhans,  406 
marrow,  127 
mast,  104 
mossy,  167 
nerve,  157,  437 

bipolar,  164 

Deiter,  157 

Golgi,  157 


Cells,  nerve,  multipolar,  164 
unipolar,  163 
neuro-epithelial,  84 

of  Cajal,  479 

of  Claudius,  538 

of  Deiter,  539 

of  Hensen,  538 

of  Kupfer,  286 

of  Martinotti,  481 

of  Paneth,  268 

olfactory,  544 

oxyntic,  261 

peptic,  259 

pigmented,  83,  104,  505 

pillar,  538 

plasma,  104 

prickle,  78 

pseudostratified,  81 

of  Sertoli,  356,  357 

solitary,  476 
of  Meynert,  481 

spider,  167 

squamous,  simple,  76 
stratified,  77 

tactile,  178,  179 

transitional,  83 

yellow,  268 
Cementoblasts,  243 
Cements,  36 
Cementum,  242 

formation,  560 
Centro-acinar  cells,  298 
Centrosome,  63 
Cerebellum,  457,  472 

nuclei  of,  472 
Cerebrum,  457,  477 
Ceruminous  glands,  429 
Cervix  of  uterus,  388 
Chambers,  anterior,  517 
posterior,  517 
vitreous,  517 
Chemical  stimuli,  67 
Chemotaxis,  67,  361 
Chloroform,  n 


568 


INDEX 


Chondrin,  121 

Chorion  frondosum,  405 

laeve,  405 
Chorionic  mesoderm,  407 

villi,  402,  403 
Choroid,  499 

Chromatin  granules,  348,  349 
Chromatic  spindle,  70 
Chromatin,  62 
Chromatolysis,  159 
Chromidia,  377 
Chromidium,  209 

Chromium  salts,  treatment  after  fixa- 
tion in,  7,  10 
Chromogen,  417 
Chromosomes,  69 
Chyle,  216,  281 
Ciliary  body,  500 

movement,  65 

muscle,  501 

processes,  500 

ring,  500 
Circulation  of  brain,  492 

of  eyeball,  517 

of  kidney,  332 

of  liver,  289 

of  lungs,  316 

spinal  cord,  492 
Circulatory  system,  1S7 
Circumanal  glands,  429 
Clark,  nucleus  of,  442 
Clearing,  10 
Clearing  agents,  for  block  technic,   11 

for  slide  technic,  32 
Clefts  of  Lantermann,  171 
Climbing  fibers,  476 
Clotting,  210 
Coarsely  granular  basophil,  208- 

eosinophil,  207 
Cochlea,  535 
Cohnheim's  fields.  142 
Colliculi,  457 
Colloid  substance,  319 
Colophonium.  35 


Colostrum,  432 
Columns  of  Bertin,  327 

of  the  spinal  cord,  445 
Compressor  urethrae  muscle,  344 
Cone  cells,  507 
Conjunctiva,  523 
Conjunctival  corpuscles,  179 
Coni  vasculosa,  356,  363 
Convoluted  tubule,  distal,  330 

proximal,  331 
Conus  medullaris,  438 
Cornea,  497 
Corneal  corpuscles,  498 

lacunae,  498 
Corneoscleral  junction,  503 
Corporo  albicantia,  457 

cavernosa,  371 
Corpus  albicans,  382 

hemorrhagicum,  382 

Highmori,  352 

luteum,  382 

spongiosum  urethras,  343,  371 
Corpuscles,  conjunctival,  179,  549 

genital,  550 

of  Golgi-Mazzoni,  181 

of  Grandy,  181 

of  Hassal,  231 

of  Herbst,  181 

of  Meissner,  181,  547 

of  Xissl,  159 

of  Ruffini,  180 

of  Vater,  182,  548 

Pacinian,  182,  548 
Corrosion,  41 
Corti,  ganglion  of,  541 

membrane  of,  539 

organ  of,  538 
Cotyledons,  407 
Counterstaining,  54 
Creosote,  S3 

Crescents  of  Gianuzi,  302,  303 
Crista  basilaris,  536 
Cristas  acusticae,  534 
Crura  cerebri,  455 


INDEX 


569 


Crusta  petrosa,  24a 
Crystalline  lens,  515 

Cumulus  ovigerus,  375 
Cupola,  533,  534 
Cuticle,  411 

of  hair,  424 
Cuticular  border,  64,  250,  267 
Cutis  vera,  415 
Cytoplasm,  58 


D 


Dammar,  35 
Dartos  fascia,  351 
Dealcoholization,  10 
Decalcification,  36 
Decidua  basilaris,  396,  408 

capsularis,  396,  402 

parietalis,  396,  408 
Decidual  cells,  407 
Dehydration,  10 
Demilunes  of  Heidenhain,  302 
Dendrites,  163 
Dental  follicle,  560 

shelf,  556 
Dentin,  239 

formation,  558 
Dentinal  fibers,  239 

pulp,  243 

sheaths,  239 

tubules,  239 
Derma,  415 

Descemet's  membrane,  498 
Dentoplasm,  377 
Diabetes  mellitus,  300 
Diaphragm  sellae,  434 
Digestion  method,  2 
Diphyodonts,  ^55 
Diplosome,  63 
Discus  proligerus,  375 
Dobie's  line,  142 
Dorsal  horns,  442 

cells  of,  442 
Ducts  of  Bellini,  327 


Ductus  cochlearis,  535 
endolymphaticus,  532 

reuniens,  533 
Duodenum,  270 
Dura,  434 

E 

Ear,  526 

bones,  529 

external,  526 

internal,  531 

middle,  527 
Ectoderm,  derivatives  of,  73 
Efferent  arteriole,  S33 
Ejaculatory  duct,  367 
Elastic  tissue,  108 
Electrical  stimuli,  66 
Eleidin,  414 
Embryonic  shield,  398 

tissue,  no 
Enamel,  237 

brown  striations,  238 

formation,  556 

germs,  556 

lines  of  Schreger,  239 

prisms,  238 

supplemental,  238 
Encephalon,  451 
Endochondral  bone,  133 
Endolymph,  532 
Endomysium,  145 
Endoneurium,  172 
Endymal  cells,  444 
Entoderm,  derivatives  of,  74 
Eosin  bodies,  475 
Epidermis,  411,  412 
Epididymis,  363 
Epidural  lymph  space,  434 
Epiglottis,  307 
Epimysium,  145 
Epineurium,  172 
Epiphysis,  492 
Epithelium,  75 

varieties  of;  76 


570 


INDEX 


E  pi  tympanum,  g 
Eponychium,  426 
Epoophoron,  385 
Erythroblasts.  44 

counting.  4S 

origin.  12S 
Erythrocytes.  129,  203 

function  of.  204 

origin  of,  129 
Esophagus.  255 

Estimating  blood  cells.  45.  46.  47.  4S 
Euparal.  35 
Excretion?.  8S 
External  auditory  canal.  526 

elastic  lamina.  194 
Exoplasm.  50 
Eyeball.  493 
Eyelashes.  522 
Eyelid.  520 


Face,  development  of.  551 
Fallopian  tube,  385 
Falx  cerebelli.  434 

cerebri.  434 
Farrant's  medium.  35 
Fat.  in 

Female  genital  system.  374 
Fenestra  cochleae.  -  _  - 

rotunda,  531 

vestibuli.  5 :  - 
Fertilization.  72 
Fetal  circulation.  409 
Fibers,  association.  481.  4S2 

commissural.  4.82 

projection.  48 1.  48 2 

of  the  spinal  cord.  449.  450 
Fibrinogen.  210 
Filiform  papilla?.  245 
Filum  terminale.  440 
Fillet.  461 
Finely  granular  basophil,  207 

eosinophil.  207 
Finger  prints.  41 S 


Fixation,  5 

Fixing  fluids  (solutions),  5 
Foramen  of  Majendie,  455 
Foramina  of  Luschka,  455 

nervosa.  541 
Formatio  reticularis,  462,  463 

alba,  464 

grisea.  464 
Fossa  navicularis.  344 
Fountain  decussation.  471 
Fovea  centralis.  512 
Free  terminals,  178 
Frozen  section,  technic.  3 
Fungiform  papillae,  246 


Gall-bladder.  294 
Ganglion,  173,  174 

spiral,  541 

sympathetic,  176 
Ganglionic  layer,  outer.  510 

inner.  511 
Gastrulation,  401 
Genital  corpuscles,  180 
Genitalia.  394 
Germinal  epithelium.  374 
Giant  cells  of  Betz.  479 
Glands,  91 

adrenal.  346 

alveolar.  96 

Bowman's,  545 

cardiac,  257,  262 
lower,  257 
upper.  257 

ductless,  101 

intestinal.  267,  274 

lacrimal.  524 

mammary,  431 

Meibomian,  521 

mixed,  96,  100 

mucous,  98 

of  Bartholin,  395 

of  Brunner,  270 

of  Cowper,  370 


INDIA 


571 


Glands  of  ELrause,  521 

of  Lieberkiihn,  267,  ^74.  276 

of  Lit  t  re,  342,  344 

of  Moll,  52a 

of  Montgomery,  433 

of  Waldeyer,  520 

salivary,  295 

sebaceous,  429 

serous,  98 

structure,  95 

sublingual,  303 

submaxillary,  300 

sweat,  428 

tubular,  92 

tubulo-alveolar,  96 

varieties,  92,  98,  100 
Glandulae  odoriferae,  372 
Glans  clitoris,  395 

penis,  371 
Glial  cells,  166,  437 

fibers,  167,  437 
Glomerulus,  326 
Glucose  mixture,  34 
Glycerin  jelly,  34 

media,  34 
Glycogen,  287 

Golgi-Mazzoni,  corpuscles  of,  181 
Graafian  follicle,  375 
Granulationes  arachnoideales,  435 
Gray  commissure,  444 

nerve  tissues,  156,  430 
Grinding,  37 
Growth,  64 

Gubernaculum  dentis,  564 
Gum  and  syrup,  34 
Gums,  235 
Gustatory  cells,  248 
hairs,  248 
pore,  247 


H 


Hair,  bulb,  420 
color,  425 
cortex,  424 


Hair,  medulla,  424 

papilla,  420 

pattern,  419 

root,  419 

shaft,  424 

sheaths,  421 
Hairs,  419 
Harmone,  299 
Haversian  canals,  125 

lamellae,  125 

systems,  125 
Heart,  187 

atrioventricular  bundle,  189 

endocardium,  187 

epicardium,  191 

myocardium,  190 

pericardium,  191 

valves,  188 
Heat,  66 

Hemapoiesis,  213 
Hemin  crystals,  211 
Hemocytometer,  45 
Hemoglobin,  211 

crystals,  211 
Hemoglobinometer,  49 
Hemokonia,  210 
Hemolymph  node,  212 
Hemometer,  Dare's,  49 

von  Fleischl's,  51 
Hemophilia,  211 
Hemosiderin,  211 
Hemotoidin,  212 
Henle's  fiber  layer,  509 
Henle's  loop,  331 
Heterodonts,  556 
Histology,  56 
Homodonts,  556 
Humor,  aqueous,  515 

vitreous,  515 
Hyalin  cells,  207 
Hyaloid  canal,  515 
Hyaloplasm,  59 
Hydrogel,  56 
Hydrosol,  56 


572 


INDEX 


Hymen,  394 
Hypophysis,  457,  490 


Ileum,  271 

Incremental  lines  of  Schreger,  240 

Incus,  529 

Inferior  quadrigeminal  level,  469 

Infiltration,  11 

aceton-paraffin,  12 

celloidin,  13 

cold,  n 

gum,  14 

paraffin,  11 
Infiltration  angle,  504 
Infundibula,  315 
Injection,  38 

intravitam,  40 

self,  40 
Injection  masses,  Berlin  blue,  38 

carmin,  38 

gelatin,  38 

Prussian  blue,  39 

wax,  41 

white,  39 

yellow,  39 
Intercalated  discs,  153 
Intercarotid  gland,  212 
Intercellular  spaces,  216 
Interglobular  spaces,  241,  559 
Interlacement  synapse,  166 
Internal  elastic  lamina,  193 
Interpeduncular  space,  456 
Interstitial  cells,  375,  384 

of  Ley  dig,  353 
Intestinal  crypts,  267,  274 
Intramembranous  bone,  136 
Intravitam  injection,  40 
Intumescentia  cervicalis,  438 

lumbalis,  438 
Investment  synapse,  166 
Involuntary  nonstriated  muscle,  147 

striated  muscle,  150 


Iodothyrin,  319 

Iris,  502 

Irritability,  66 

Islands  of  Langerhans,  299 

Iter,  469 


Karyolysis,  215 
Karyoplasm,  62 
Karyorrhexis,  215 
Karyosome,  61 
Karyotome,  62 
Keratin,  413,  414 
Keratinization,  78 
Keratohyalin,  414 
Kidney,  323 

circulation  of,  332 
function  of,  336  j 
Kuskow's  solution,  3 


Labia,  majora,  395 

minora,  395 
Labyrinth,  membranous,  532 

of  kidney,  325 

osseous,  532 
Lacrimal  duct,  525 

gland,  524 

sac,  525 
Lacteal,  268,  281 
Lamina  cribrosa,  497 

fusca,  497 

suprachoroidea,  499 
Langhans,  cell-layer  of,  406 
Large  intestine,  274 
Laryngopharynx,  254 
Larynx,  307 
Lateral  geniculate  bodies,  458 

horns,  442 

recesses  of  fourth  ventricle,  455 
Layer  of  Henle,  423 

of  Huxley,  423 


INDEX 


573 


Lemniscus,  461 
Leukocytes,  129,  206 

origin  of,  129 
Lid  muscle  of  M tiller,  522 
Ligamentum  spiralc,  536 
Light,  66 

Limbs  of  Henle's  loop,  331 
Limbus,  537 
Lines  of  Schrcger,  239 
Lingua]  tonsils,  250 
lip,  233 
Liquor  folliculi,  375 

sanguinis,  210 
Liver,  283 

circulation  of,  289 

function  of,  291 

of  pig,  284 
Long  posterior  ciliary  arteries,  519 
Loop  of  Henle,  331 
Lungs,  311 

circulation  of,  316 
Lunula,  426 
Luschka's  cartilage,  308 

gland,  212 
Lymph,  216 

capillaries,  217 

ducts,  217 

nodes  (glands),  221 
functions  of,  224 

organs,  218 
Lymphatic  system,  216 
Lymphocytes,  206 
Lymphoid  tissue,  114,  218 

agminated  nodules,  220 

diffuse,  218 

lymph  nodes,  221 

solitary  nodules,  219 

M 

Maceration,  2 
Macula  acusticae,  533 

lutea,  512 
Male  genital  system,  351 


Malleus,  530 

Malpighian  corpuscles,  326 

pyramids,  327 
Mammary  gland,  431 
Mammilla,  432 
Margarin  crystals.  112 
Marrow,  red,  127 

yellow,  127 
Maturation,  72 

in  female,  380 

in  male,  359 
Mayer's  albumen,  53 
Mechanical  stimuli,  66 
Medial  lemniscus,  463 
Median  longitudinal  bundle,  464,  466, 

469,  471 
Mediastinum  testis,  353,  354 
Medullary  cards,  223,  231 

cavity,  127 

pyramids,  327 

ray,  325 

veli,  455 
Megakaryocytes,  131,  215 
Megaloblast,  214 
Meibomian  gland,  521 
Melanin,  417 
Membrana  eboris,  558 

limitans  olfactoria,  543 

nictitans,  523 

preformativa,  558 

reticularis,  539 

tectoria,  539 

tympani,  529 
secundaria,  527 
Membrane  of  Bruch,  500,  503 

of  Reissner,  535 
Membranes,  408 
Membranous  urethra,  343 
Menstruation,  390 
Mesencephalon,  455 
Mesoderm,  derivatives  of,  74 
Metabolism,  64 
Metallic  reflex,  500 
Microsomes,  59 


574 


INDEX 


Midbrain,  455,  469 
Midolivary  level,  462 
Milk,  432 
Mitochondria,  60 
Mitosis,  68 

phases,  68 
Morula,  73,  396 
Motion,  65 

Motor  decussation,  460 
terminals,  184 

in  cardiac  muscle,  186 
in  glands,  186 
in  smooth  muscle,  186 
in  voluntary  muscle,  1S4 
Mounting  media,  34 
Mouth,  234 

Mucous  membranes,  84 
structure,  86 
typic,  86 
tissue,  no 
Miiller,  lid-muscle  of,  522 

ring  muscle  of,  502 
Muscle,  A,  145 

contraction,  143 
development  of,  1 54 
fiber,  140 
red,  143 
white.  143 
regeneration  of,  1 5  5 
of  Riolanus,  522 
spindles,  183 
tissue,  139 
Muscularis  mucosae,  87 
Myelencephalon,  452 
Myelin  sheath,  :_: 
Myelocytes,  1 
Myeloplaxes,  131 


X 


Nail  bed,  427 
body,  426 
fold,  426 


Xail  groove,  426 

wall,  426 
Xails,  426 
Xares,  306 
Xasal  mucosa,  306 
Xasmyth's  membrane,  245 
Nasofrontal  process,  551,  554 
X'asopharynx,  254,  307 
Xerve,  172 

cells,  437 

fibers,  amyelinated,  168 
gray,  168,  169 
myelinated,  169 
white,  169 

organs,  17S 
cm  434 

tissue,  156 
Nerves,  degeneration  of,  177 

sympathetic,  176 
Neubauer's  ruling,  46 
Xeuman's  sheaths,  239 
Xeurenteric  canal,  402 
Xeurocyte,  157 
Xeurofibrils,  158 
X'euroglia,  166,  437 

of  spinal  cord,  445 
Neurolemma,  172 
X'euron,  157 
Xipple,  432 
Xissl's  corpuscles,  159 

degeneration,  159 
Xode  of  Ranvier,  171 
Xotochord,  402 
Xotochordal  invagination,  401 
Xuclear  layer,  509 

membrane,  62 

stains,  16 
Xucleolus,  63 
Xucleus,  61 

of  Clark,  442 

cuneatus,  454,  461 

gracilis,  454,  461 

of  Stilling,  442 
Xymphje,  395   . 


INDEX 


575 


o 

Oblongata,  452,  459 
Odontoblasts,  243,  558 
Odoriferous  glands,  sexual,  429 
Oil,  anilin,  33 

anilin-xylol,  33 
carbol-xylol,  33 
cedar,  33 
clove,  33 
of  bergamot,  33 
origanum,  33 
thyme,  23 
Olfactory  glomeruli,  488 
lobe,  488 
mucosa,  543 
Olive,  464 
Oocyte,  379 
Oogenesis,  379 
Optic  chiasm,  457 
nerve,  513 
tracts,  458 
Ora  serrata,  505 
Organ  of  Corti,  538 
of  Giraldes,  373 
of  smell,  543 
Oropharynx,  254 
Osmic  acid,  8 
Ossification  groove,  136 
Osteodentin,  241 
Otoconia,  533 
Otolith  membrane,  533 
Otoliths,  533 
Ovary,  374 
Oviduct,  385 
Ovuli  Nabothi,  388 
Oviparous,  404 
Ovulation,  383 
Ovular  decidua,  402 
Ovum,  71,  376 


Pacchionian  bodies,  435 
Pacinian  corpuscles,  182 


Palate,  235 

development  of,  554 
malformations  of,  554 
Palatal  tonsil,  252 
Panniculus  adiposus,  416 
Pancreas,  297 
Pancreatic  islands,,  299 
Pancreatin,  3 
Papilla,  nervi  optica),  512 
Papillae,  245 

filiform,  245 
fungiform,  246 
vallate,  246 
Papillary  ducts,  332 
Paradidymis,  373 
Paraplasm,  60 
Parathyreoids,  321 
Pareleidin,  413,  414 
Paroophoron,  385 
Parotid  gland,  296 
Parovarium,  385 
Pars  anterior,  490 

dorsalis  pontis,  466 
flaccida,  529 
intermedia,  491 
nervosa,  491 
optica,  505 
tensa,  529 
Pathway,  direct  motor,  482 
direct  sensor,  484 
indirect  motor,  483 
muscle  sense,  487 
respiration,  488 
touch,  pain,  temperature,  484 
Pectinate  ligament,  504 
Penile  urethra,  344 
Penis,  371 

Peridental  membrane,  244,  560 
Perilymph,  532 
Perimysium,  143 
Perineurium,  172 
Periosteal  bone,  134 
Peripheral  nerve  system,  172 
system,  437 


576 


INDEX 


Perspiration,  429 

Peyer's  patch,  116,  271 

Pharyngeal  tonsil,  254,  307 

Pharyngotympanic  tube,  530 

Pharynx,  254 

Pia,  436 

Pigment  layer,  505 

Pineal  body,  492 

Pinna,  526 

Pituitary  body,  49c 

Placenta,  396,  407 

Placentas,  varieties,  408 

Placental  decidua,  396 

Placentoblast,  402 

Plasmatic  stains,  19 

Plasmosome,  63 

Plastids,  59 

Pleurae,  311 

Plexus,  myenteric,  280 

of  Auerbach,  280 

of  Meissner,  281 

submucous,  281 
Plicae  circulares,  274 

palmatae,  388 

semilunaris,  523 

ventriculares,  308 

villosae,  259 

vocales,  308 
Polar  bodies,  380 
Polyphyodonts,  555 
Pons,  454,  465 

fifth  nerve  level,  467 

lower  section,  465 

tegmental  portion  of,  454 

upper  level,  468 
Portal  canals,  286 

systems,  286 
Precapillary,  198 
Primitive  erythrocyte,  214 

lymphocyte,  214 
Prominentia  spiralis,  536 
Prostate,  367 
Prostatic  concretions,  369 

urethra,  343 


Prostatic  utricle,  343 
Protection,  89 
Protoplasm,  56 

composition,  56 
Protoplasmic  movement,  65 
Pyloric  canal,  262 
Pyramidal  decussation,  453 
Pyramids  of  Ferrein,  325 
Pyrenoid  substance,  417 
Pyroxylin,  13 
Pupil,  503 


Quadrigemina,  456 


R 


Rectal  valves,  276 

Rectum,  275 

Red  blood-cells,  counting,  45 

nucleus,  470 
Renal  corpuscles,  326 

tuft,  326 
Renculus,  324 
Repair  dentin,  241 
Reproduction,  67 
Respiratory  system,  306 
Restiform  bodies,  457 
Rete  testis,  356,  363 
Retia  mirabilia,  46,  200 
Reticular  layer,  outer,  509 

inner,  511 
Reticulum,  no 

digestion  method,  3 
Retina,  504 
Retinal  artery,  517 
Rhodopsin,  507 
Ring  muscle  of  Miiller,  502 
Ringer's  solution,  1,  36 
Riolanus,  muscle  of,  522 
Rod  cells,  507 


INDKX 


577 


Saccule  >»i  larynx,  308 
Sacculus,  532 
Salivary  glands,  295 
Sarcomere,  142 
Sarcoplasm,  140 
Sarcostyle,  141 
>^  ala  media,  535 

tympani,  535 

vestibuli,  535 
Sclera,  495 
Scrotum,  351 
Sebaceous  glands,  429 
Sebum,  430 
Secretion,  87 
Sectioning,  15 

celloidin,  15 

frozen,  3 

paraffin,  15 
Self  injection,  40 
Semen,  361 

Semicircular  canals,  534 
Seminal  vesicles,  366 
Seminiferous  tubules,  355 
Sense  of  smell,  544 

of  taste,  546 

of  touch,  547 
Sensor  decussation,  461 
Serous  membranes,  89 

structure,  90 
Sex  determination,  73 
Sheath  of  Henle,  173 
Short  posterior  ciliary  arteries,  517 
Sinus  lactiferous,  431 
Sinuses,  200 
Sinusoids,  200 
Skin,  411 
Slide  technic,  53 
Small  intestine,  265 
Smegma,  372 
Smooth  muscle,  147 
Solitary  nodules,  115 
Solution,  Bouin's,  9 
37 


Solution,  chromic  acid,  7 
decalcifying,  36 
Flemming's,  8 

formalin,  8 

Golgi's,  8 

Hayem's,  46 

Heidenhain's,  6 

Helly's,  7 

Kleinenberg's,  9 

Kuskow's,  3 

Mayer's,  36 

Muller's,  6 

nitric  acid,  9 

osmic  acid,  8 

phloroglucin-nitric  acid,  36 

picric  acid,  37 

picrosulphuric,  9 

potassium  bichromate,  6 
formalin,  7 

Ringer's,  1 

Sherrington's,  46 

Tellyesniczky's,  7 

Toisson's,  4^ 

trichloracetic  acid,  37 

Zenker's,  6 

Zenker-formalin,  7 
Somatopleure,  401 
Spaces  of  Fontana,  504 
Spermioblast,  357 
Spermiogenesis,  359 
Spermiogonia,  356,  359 
Spermium,  72,  357 
Spinal  cord,  438 

functional  division  of,  451 

nerve,  451 
Splanchnopleure,  401 
Spleen,  224 

functions  of,  230 
Splenic  circulation,  228 

corpuscles,  227 

phagocytes,  226 

pulp,  225 
Spongioplasm,  58 
Squamous  cells,  simple,  76 


578 


INDEX 


Squamous  cells,  stratified,  77 
Staining,  16 

tubules  of  the  kidney,  40 
Stains,  acid,  19 

fuchsin,  21 
amyloid,  30 
basic,  16 

Bismark  brown,  18 
carmin,  alum,  20 

borax,  19 

para,  20 

picro,  20 
capsicum  red,  29 
chromaffin  granules,  32 
chromatic,  16 
cyanin,  29 
Ehrlich-Biondi,  21 
elastica,  Weigert's,  28 
eosin,  19 
for  fat,  capsicum  red,  29 

cyanin,  29 

osmic  acid,  29 

Sudan  III,  29 
for  white  fibrous  tissue,  29 
glycogen,  30 

Gage,  31 
gold,  Apathy's  method,  24 

Ranvier's  method,  24 
hematoxylin,  acid,  17 

Delafield's,  17 

Harris',  17 

iron,  25 

Weigert's,  25 

Weigert-Pal,  25 
mast  cells,  31 
methyl  green,  iS 
methylene  blue,  18,  44 

polychrom,  18 
mitochondria,  31 

Benda's  method,  32 
muchematein,  30 
mucin,  30 
myelin,  Marchi,  27 

Weigert,  25 


Stains,  myelin,  Weigert-Pal,  26 

neuroglia,  27 

Nissl's,  28 

nuclear,  16 

orange  G,  21 

osmic  acid,  29 

picric  acid,  19 

picrocarmin,  20 

picrofuchsin,  19 

plasma  cells,  31 

plasmatic,  19 

reticulum  (Mallory's),  29 

Ruthenium  red,  2 1 

safranin  O,  18 

silver,  of  endothelial  cells,  22 
of  lymph  spaces,  22 
of  nerve  cells,  22 
of  neurofibrils,  Bielschowsky,  22 
Golgi,  22 

silver  hemateinate,  16 

special,  21 

Sudan  III,  29 
Stapedius  muscle,  530 
Stapes,  530 

Stilling,  nucleus  of,  442 
Stomach,  258 
Stomodeum,  551 
Straight  collecting  tubules,  331 
Stratum  compactum,  408 

granulosum,  413,  414 

lucidum,  414 

Malpighii,  413 

papillare,  415 

reticulare,  416 

spinosum,  413 

vasculare,  389 
Striation  of  Baillarger,  481 

of  Bechtereff,  481 
Subarachnoid      lymph      space,      435, 

436 
Subdural  lymph  space,  435 
Subendothelial  tissue,  91 
Sublingual  gland,  303 
Submaxillary  gland,  300 


INDEX 


579 


Substantia  gelalinosa  centralis,  445 
Rolandi,  443,  445,  461 

nigra,  469 

spongiosa,  445 
Sudoriferous  glands,  428 
Sulcus  spiralis,  538 
Superior  quadrigeminal  body,  470 
Suprachoroidal  space,  499 
Suprarenal  body,  346 
Sweat-glands,  428 
Sweat-pore,  429 
Synapse,  166 
Syncytium,  75,  404,  4°5 


Tactile  corpuscles,  179,  181 

Tapetum  cellulosum,  500 
fibrosum,  500 

Tarsal  plate,  520 

Taste-buds,  247,  308,  546 

Technic,  1 
blood,  41 
frozen  section,  3 
rapid  method,  4,  16 
slide,  53 

Teeth,  237 

development  of,  551 
eruption  of,  560,  562 
malformations  of,  564 
permanent,  555,  560 
temporary,  555 

Teichman's  crystals,  211 

Tendon,  107 

spindles,  184 

Tensor  tympani  muscle,  530 

Tentorium  cerebelli,  434 

Thrombin,  210 

Thrombocytes,  209 

Thymic  corpuscles,  231 

Thymus  body,  230 
functions  of,  231 

Thyreoid  body,  319 

Tigroid  bodies,  159 


lies,  75 

adipose,  III 

areolar,  103 

connective,  101 

elastic,  108 

embryonic,  no 

epithelial,  75 

erectile,  371,  394 

lymphoid,  114 

mucous,  no 

muscle,  139 

nerve,  156 

reticulum,  no 

retiform,  no 

white  fibrous,  105 
Tome's  fibers,  240 
Tongue,  245 
Tonsils,  lingual,  250 

palatal,  252 

pharyngeal,  254 

tubal,  254,  307 
Trachea,  309 
Tracts  of  the  spinal  cord,  446,  447,  44^, 

449 
Trapezium,  467 
Trigone  vesicae,  340 
Triploblast,  398 
Trophocyte,  146,  357 
Trophoderm,  396 
Trophodermal  villi,  402 
Trophospongium,  61 
Tubal  tonsil,  254,  307 
Tuber  cinereum,  457 
Tuberculum  cinereum,  461 
Tunica  adventitia,  194 

albuginea,  352,  374 

intima,  192 

media,  193 

propria,  86 

vaginalis,  352,  354 
Tympanic  cavity,  527 

membrane,  529 
Tyrosin,  417 
Tyrosinase,  417 


58o 


INDEX 


U 

Ultimate  lobule  of  lung,  313 
Umbilical  cord,  408 
Ureter,  337 

pelvis  of,  336 
Ureter-sheath,  339 
Urethra,  female,  342 

male,  343 
Urethral  crest,  343 

gland,  343,  344 
Urinary  system,  323 
Urine,  336 
Uterus,  387 

cervix  of,  388 

glands  of,  388 
Utriculus,  532 


V 


Vagina,  393 
Vaginal  orifice,  394 
Vallate  papillae,  246 
Vasa  efferentia,  356,  363 
Vasa  recti,  356 
Vas  deferens,  365 
Veins,  201 

valves  of,  201 
Venae  rectae,  335 

stellatae,  333 
Venous  arches,  335 
Ventral  horns,  440 

cell  groups  of,  440 
Ventricle  of  larynx,  308 
Vermis,  457 

Vestibule,  306,  394,  532,  543 
Vibrissas,  306,  543 
Villi,  chorionic,  402,  403 

intestinal,  268 


Villi  of  oviduct,  386 

trophodermal,  402 
Visual  purple,  507 
Vitreous  humor,  515 
Viviparous,  404 
Vocal  cords,  false,  308 

true,  308 
Voluntary  striated  muscle,  139 

W 

Wharton's  jelly,  409 
White  blood  cells,  129,  206 
counting,  47 
differential,  47 
commissure,  445 
nerve  tissue,  437 
substance  of  spinal  cord,  445 
Wright's  method,  4 
stain,  43 

X 

X-chromosome,  360 
Xylol,  11,  33,  54 


Yellow  cells,  268 
spot,  512 


Zona  fasciculata,  347 
glomerulosa,  347 
granulosa,  375 
pellucida,  375 
reticularis,  347 

Zymogen,  260,  298 


Date  Due 

' 

• 

f> 

1 

flti 


